Mutombo posted two messages and photos on his Facebook page, saying, "I am safe here" and "I am fine."
His charitable foundation also posted a message on Facebook, saying that the former NBA star "was thankfully unharmed."
Multiple explosions rocked the Zaventem international airport and the Brussels subway system, killing at least 31 people. The Islamic State group claimed responsibility for the attacks, saying in a posting from the group's Amaq news agency that its extremists opened fire in the airport and "several of them" detonated suicide belts.
Mutombo, 49, was an eight-time All-Star during his 19-year NBA career and was inducted into the Naismith Basketball Hall of Fame last year.
He played for the 76ers from 2001 to 2002.
Belgium's national soccer team responded to the attacks by canceling its scheduled practice session Tuesday.
The Royal Belgian Football Federation posted an announcement on the Twitter account for its national team, saying, "Football is not important today" and that "our thoughts are with the victims."
Belgium will host Portugal in a friendly match on March 29 at the King Baudouin Stadium in Brussels. The game is scheduled as a warm-up for both teams ahead of this year's European Championship in France.
The Portuguese soccer federation said it was in contact with Belgian authorities about security arrangements for the match.
President Barack Obama was asked by ESPN's Karl Ravech during the Rays-Cuba baseball game to address the nation about the attacks.
"I had a chance to talk to the Belgian prime minister earlier this morning, right after the explosion had happened, and this is just one more example of why the entire world has to unite against these terrorists -- that the notion that any political agenda would justify the killing of innocent people like this is something that's beyond the pale," Obama said."We are going to continue with the over 60 nations that are pounding ISIL and are going to go after them. ... In the meantime, obviously, our thoughts and prayers with those who were lost and hoping for a speedy recovery to those who've been injured."
French Interior Minister Bernard Cazeneuve said the explosions are a reminder that a "very high security level" will be required during the European Championship. He said the measures taken to guarantee "collective security" at the June 10-July 10 tournament will include the mobilization of specially trained emergency staff, police forces and firefighters.
The two airport blasts, at least one of them blamed on a suicide bomber, left behind a chaotic scene of splattered blood in the departure lounge as windows were blown out, ceilings collapsed and as travelers streamed out of the smoky building.
About an hour later, another bomb exploded on a rush-hour subway train near the European Union headquarters. Terrified passengers had to evacuate the train through darkened tunnels to safety.
"What we feared has happened," Belgian Prime Minister Charles Michel said. "In this time of tragedy, this black moment for our country, I appeal to everyone to remain calm but also to show solidarity."
Belgium raised its terror alert to the highest level, diverting planes and trains and ordering people to stay where they were for most of the workday.
Sebastien Bellin, a European professional basketball player who played collegiately in the United States, was injured in one of the airport explosions, according to his former team in Belgium.
One international soccer player was at the Zaventem airport when the explosions were reported. Norwich forward Dieumerci Mbokani, who is from Congo, was "unharmed but shaken by the tragic events," the English club said in a statement.
Mbokani was visiting family in Brussels, where he played for Anderlecht for two seasons until 2013.
Belgian golferThomas Pieterslives in Antwerp, Belgium, and is playing at the WGC-Dell Match Play Championship in Austin, Texas.
"I woke up at 6 a.m. and my phone was just buzzing,'' Pieters told ESPN's Bob Harig. "Everybody was asking me, 'Is your family OK?' And I kind of knew what was going on, so I opened the news sites and it was just one of the worst days to wake up.
"Even when it happened in Paris, it's close, but it's not right near your people. And now it happens to somewhere I go almost every time I fly out. That's where I go. It's shocking to see so many images and the videos. It's a sad day.''
The explosions occurred four days after Salah Abdeslam, a prime suspect in the Nov. 13 Paris attacks that killed 130 people, was arrested in Brussels.
ESPN FC, ABC News, ESPN's Bob Harig and The Associated Press contributed to this report.