A 4ft rocket propelled grenade (RPG) isn't the typical thing you'd expect to find in the backseat of a teen's car, especially in a small Californian town just outside of San Francisco.

But that's exactly what police discovered after stopping a 15-year-old schoolboy for a small traffic violation in Novato, California Tuesday morning, reports KTVU.

Struck with alarm, police called the University of California Police Department's bomb squad and evacuated the surrounding streets, reports The Daily Californian.

Police are still surprised how the teen got his hands on the rocket propel grenade in the first place.

"It's unusual for Novato to recover an RPG from the back of a vehicle," Novato Police Cpl. Nick Frey told KTVU.

But according to the Daily Mail, the boy's brother may be linked given he works on a military base nearby.

No ammunition was reportedly found, which is now at the Travis Air Force Base. As for the teen boy? He's now being held in a juvenile detention center on felony charges, including possession of a destructive device.

These type of rocket launchers are typically carried by soldiers and insurgents in Afghanistan. Just last month a NATO helicopter was downed by a RTG, according to CNN reports. See the YouTube video below of military soldiers using a similar rocket propelled grenade in action.