Lynch, who played in the Pro Bowl one week ago, was arrested Wednesday in Culver City, Calif., on felony charges for possession of a concealed firearm.
The Culver City Police Department on Sunday afternoon released a brief statement with details of the arrest. The statement noted officers spotted three men in a 2006 Mercedes Benz and recognized Lynch as the Bills' running back.
"A subsequent field investigation led to the discovery of a loaded firearm," the report said. "The officers determined the gun belonged to Lynch and he was arrested for possession of a concealed firearm."
Lynch's lawyer, M. Gerald Schwartzbach, said his client was not involved in a traffic incident. Schwartzbach said the player was in California to visit friends.
The Los Angeles County Sheriff Department's inmate database says Lynch was booked at 7:12 p.m. and was released on a $35,000 bond at 8:45 p.m.
"We are aware of it and will monitor it," NFL spokesman Greg Aiello wrote in an e-mail to ESPN.com.
Gun safety is a significant issue in the NFL. It has been a hot topic since New York Giants receiver Plaxico Burress was arrested on two felony charges in December after accidentally shooting himself at a Manhattan nightclub.
"We can confirm that Marshawn was arrested in California and has retained an attorney," Bills vice president of communications Scott Berchtold said in a statement. "We are in the process of trying to gather the facts and will not offer a comment while that process is ongoing."
Lynch's agent didn't return ESPN.com's request for a comment.
Lynch last summer was the subject of a hit-and-run investigation in Buffalo after his luxury SUV struck a woman in the street and sped away.
After nearly a month of posturing from Lynch's lawyers and the Erie County District Attorney, Lynch paid a $100 fine in a plea agreement. He didn't face criminal charges because the woman's injuries weren't serious enough. She sustained a bruised hip and cut to her thigh that required seven stitches at a local hospital.
In 2006, as Lynch was about to enter his junior season at California, he was the target of a drive-by shooting outside his prep alma mater, Oakland Technical. Police determined Lynch was the victim of mistaken identity.
Lynch, who will turn 23 in April, ran for 1,038 yards and eight touchdowns last season. He also caught 47 passes for 300 yards and a touchdown.