The agency provided few details, saying the investigation into Buford 'Bucky' Rogers, 24, was "ongoing".
"The FBI believes that a terror attack was disrupted by law enforcement personnel and that the lives of several local residents were potentially saved," the agency said in a statement.
"The terror plot was discovered and subsequently thwarted through the timely analysis of intelligence and through the cooperation and coordination between" multiple law enforcement agencies, the FBI said.
Rogers, who has a conviction on burglary charges, is prohibited from owning firearms but admitted to having fired the assault rifle on two occasions at a nearby gun range, according to charging papers.
He was arrested "without incident" on weapons charges.