The men were picked up in a raid on a house in Sarghoda in the eastern province of Punjab, police officer Tahir Gujjar said, adding that three of the men are of Pakistani descent, one is of Egyptian descent and the other is of Yemeni heritage.
Regional police chief Mian Javed Islam told The Associated Press that the men were between the ages of 18 and 20 and had spent the past few days in the city, which is near an air base about 125 miles (200 kilometers) south of the capital, Islamabad.
He said they were being questioned and it was premature to discuss the reason for the detentions.
But two U.S. officials familiar with the case said the five are believed to be young men from the Washington area who went missing at the end of November.
The FBI has been searching for the men since their families reported them missing and expressed fears they may have gone to Pakistan, according to the two U.S. officials. The two are familiar with the case and spoke on condition of anonymity because they were not authorized to discuss it publicly.
One of the men was a dental student at Howard University, according to the officials.
The officials said one of the group - they did not say which one - left behind what investigators believe was a farewell video message, in which he talks about defending Muslims and shows images of U.S. casualties.
U.S. Embassy spokesman Rick Snelsire said officials there were aware of the reported arrests, but could not confirm them.
A report on the Web site of the Pakistani newspaper The News said one only one of the men was American.
Quoting a senior police officer, the report said it "was quite a possibility that they (the five men) were engaged in acts of terrorism."
Pakistan has many militant groups based on its territory and the U.S. has been pressing the government to crack down on extremism. Al-Qaida and Taliban militants are believed to be hiding in safe havens in lawless tribal areas near the Afghan border.
Khan reported from Islamabad; Barrett from Washington.