A Roslindale man was arrested Saturday night when a handgun allegedly fell out of his shorts during a traffic stop, Boston police said.

Jeffrey Paul, 29, was driving near Harold and Ruthven streets in Roxbury when he was pulled over at 7:45 p.m. for a traffic infraction, police said in a statement.

His passenger, Kesner Leneus, 24, of Boston, was wanted on a warrant for disorderly conduct and was arrested, police said.

While officers were placing Leneus in handcuffs, Paul began “moving around in a suspicious manner inside the car’’ and was then asked to step out of the vehicle. At that point, a loaded .25-caliber Raven handgunfell out of his shorts, police alleged. Paul was arrested without incident.

Paul was arraigned in Roxbury Municipal Court on charges of unlawful possession of a firearm, unlawful possession of ammunition, and carrying a loaded firearm. He pleaded not guilty and was ordered held on $12,500 bail.

It was his second arrest for illegal possession, police said.

Paul was convicted of illegal gun possession in 2008 and sentenced to three years in prison, according to Jake Wark, a spokesman for Suffolk District Attorney Daniel F. Conley.

Dylan McGuinness can be reached at dylan.mcguinness@globe.com. Follow him on Twitter @DylMcGuinness.