The agency said further testing was being conducted on the substance, but it is "within normal values."
White powder also was found in a letter sent to former New York City Mayor Rudolph Giuliani's business in New York City, where police said preliminary tests showed it posed no threat.
A federal law enforcement official, who wasn't authorized to comment publicly and spoke on condition of anonymity, said powder from one envelope tested positive for baking soda. It's not clear where that letter was sent.
Hackensack University Medical Center received a number of people for evaluation because they came in contact with the letters, but a hospital spokeswoman said there were no reported illnesses or injuries.
In New Jersey, the suspicious mailings went to at least five hotels, Carlstadt Police Detective John Cleary said.
The mailings arrived at an Econo Lodge in Carlstadt, a Homestead Suites hotel in East Rutherford and a Renaissance Inn in Rutherford, Cleary said. Investigators intercepted additional envelopes from a mail truck before they reached a Holiday Inn Express and Hampton Inn in Carlstadt, he said.
At the Homewood Suites, General Manager Thomas Martucci said the letter sent to his motel contained yellow powder and a typed letter inside referencing al-Qaida and the Dallas FBI.
"It was nonsense," he said.
Lauren Wallace, a jet company employee from Los Angeles staying at the Homewood Suites, said she saw hazardous-material trucks outside and was shooed back from the lobby to her room around 11:15 a.m. by a hotel employee. She said she was allowed out of her room about 40 minutes later.
"I think it could be a distraction or a hoax," said Chris Murray.
Chris Murray is the owner of the Quality Inn Lyndhurst, one of several hotels around MetLife Stadium that received a letter containing a suspicious white substance.
"About 1:00 p.m., a detective came into my office and I found the letter, and he told me I have to leave my office. They said there might be some substance inside the letter. I didn't look at it. It was still wrapped up in the rubber band."
The joint terrorism task force and hazardous materials crews in yellow suits responded to the Quality Inn and other hotels near the stadium.
"Believe me, if we felt there was danger, we wouldn't be standing here right now," said Chief James O'Conner. "We're not seeing any evacuation of the premises, so there's no danger."
Police were called to Giuliani's firm near Rockefeller Center after a worker opened the suspicious letter addressed to Giuliani around 10:30 a.m. Friday, police said. Eight mailroom workers underwent decontamination as a precaution.
A representative for Giuliani's firm said the substance was found to be nonhazardous.
The massive response is an indication of the enormous security presence assembled for the Super Bowl.
4000 officers in all from dozens of federal state and local agencies will be protecting the 80,000 people in MetLife stadium for the first cold-weather Super Bowl, as well as the mass transit systems that will bring fans to and from the game.
"Our SWAT team our divers our rescue personnel in coordination with our aviation and our Marine division has done extensive training over the last several months," said Lt. Col. Edward Cetnar, New Jersey State Police.___
Associated Press writers Alicia A. Caldwell in Washington and Geoff Mulvihill in Trenton contributed to this report.