The FBI said Yonathan Melaku, 22, of Alexandria, Va., was arrested early Friday "carrying items which caused initial concerns about the public's safety." His car was found parked in a wooded area near the Pentagon, but Arlington County Fire officials and the FBI determined the vehicle posed no immediate threat.
Bomb experts were summoned to Arlington because of materials found in Melaku's backpack and determined the substances were "non-explosive and inert."
"The materials in the backpack will undergo further testing at the FBI Laboratory in Quantico, Va.," the FBI said in a release.
The FBI and Fairfax County police also searched Melaku's apartment.
"At this time, law enforcement believes Melaku acted alone and that there were no other locations or activity involved," the FBI said.
Melaku joined the Marine Corps Reserve Sept. 4, 2007, and holds the rank of lance corporal. He is a motor vehicle operator with Combat Engineer Support Company, 4th Combat Engineer Battalion, 4th Marine Division, Marine Forces Reserve.
Melaku was previously awarded the National Defense Service Medal and the Selected Marine Corps Reserve Medal. He has not been deployed overseas.
Melaku was being held by the U.S. Park Police.
CBS reported Melaku was carrying a notebook contained the phrases "al-Qaida," "Taliban rules" and "Mujahid defeated croatian forces," but he is not believed to have been plotting a terrorist act.