The man is believed to be a naturalized U.S citizen from Ethiopia.
Al Qaeda-related statements, a backpack containing ammonium nitrate, and spent 9mm shells were found in the car, authorities say.
FBI Special Agent Brenda Heck described the man as being “approximately in his twenties” and said he was “not forthcoming” when he was arrested.
Law enforcement work near the Pentagon after a suspicious vehicle forced multiple road closures Friday.
US Park Police then searched for the man’s vehicle. A short time later, the car — described by Heck as a red 2011 Nissan — was located near the Pentagon.
The car was searched by bomb experts, Heck said, who did not find “significant explosive related materials.”
Agents also found a backpack near the vehicle containing “suspicious items” that Heck said were a “non-explosive unknown material.”