Ryan Kelly Chamberlain II, 42, was last seen Saturday south of the city, the agency said in a statement.
“We don’t know the intent or motive yet,” FBI agent Peter Lee told reporters, stressing there was no threat to public safety.
Chamberlain was described as a white male, 6 feet, 3 inches tall, and 225 pounds, with brown hair and blue eyes. He was last seen driving a white 2008 Nissan Altima with either a California or Texas license plate.
He should be considered armed and dangerous, the FBI said.
Chamberlain’s block was closed for some 15 hours over the weekend as investigators searched and cleared the area, CNN affiliate KTVU reported.
It was not immediately clear what led them to that site.