Jake J. Brahm, of Wauwatosa, Wis., surrendered to the U.S. Marshal's Service in Milwaukee on Friday morning. He was charged in a sealed criminal complaint filed Thursday in Newark, U.S. Attorney Christopher Christie said.
One of the stadiums allegedly targeted was Giants Stadium in East Rutherford, N.J.
Brahm was scheduled to make a court appearance later Friday in Milwaukee. The defendant is not believed to be a terrorist threat, CBS News reports.
He was first taken into custody by police in Wauwatosa, Wis., on Wednesday, based on information authorities received that Brahm was the source of the Internet threat to bomb football stadiums, federal authorities said.
FBI agents interviewed him that night, and the FBI said Thursday it had determined the threats were a hoax.
A joint statement from the FBI and Homeland Security Department said fans "should be reassured of their security as they continue to attend sporting events this weekend."
An FBI official in Washington, who spoke on condition of anonymity because the case is still under investigation, told The Associated Press that the man acknowledged posting the phony stadium threat as part of a "writing duel" with a man from the Brownsville, Texas, area to see who could post the scariest threat.
The Texas man corroborated the story, the official said. Investigators also searched the Milwaukee man's computer, the official added.
"I don't think it was put out there to be real," said FBI agent Linda Krieg in Milwaukee. "Whoever put it out there is not in a position to actually carry through on it."
The threat, dated Oct. 12, appeared on the Web site "The Friend Society," which links to various online forums and off-color cartoons. Its author, identified in the message as "javness," said trucks would deliver radiological bombs Sunday to stadiums in Miami, Atlanta, Seattle, Houston, Cleveland, Oakland, Calif., and the New York City area, and that Osama bin Laden would claim responsibility.
The agency alerted authorities Wednesday in the cities mentioned, as well as the NFL and the National Collegiate Athletic Association. But the FBI and Homeland Security said there was no intelligence indicating such an attack might be imminent.
Milwaukee police contacted the FBI about the 20-year-old man Wednesday night.
The man questioned did not appear to have any ties to terrorist groups, according to the official who spoke on condition of anonymity.
NFL spokesman Greg Aiello said stadiums are well protected through "comprehensive security procedures" that include bag searches and pat-downs.