The official said Noor Salman was taken into custody Monday morning in the San Francisco area and is facing charges in Florida including obstruction of justice. A Twitter post from the United States attorney's office in Orlando said Salman will make her initial appearance Tuesday morning in Oakland, California.
The official was not authorized to discuss the matter publicly and spoke on condition of anonymity.
Noor Salman moved to the San Francisco area after her husband, Omar Mateen, was killed in a shootout with SWAT team members during the June 12 massacre at the Pulse nightclub in Orlando.
FBI agents repeatedly questioned Salman in the aftermath of the shooting about whether she had advance knowledge of her husband's plans. She told The New York Times in an interview published in November that she was unaware that Mateen planned to shoot up the nightclub.
He was the only shooter, and by the time a three-hour standoff between Mateen and law enforcement had ended, 49 patrons were killed and another 53 people required hospitalization.
Mateen pledged allegiance to the Islamic State group in a 911 call to emergency officials during the standoff. He also made a series of Facebook posts and searches before and during the attack.
The Times first reported on the arrest.
Last month, Salman filed a petition in a California court to change the name of the son she had with Mateen.