Police said Lynch was arrested Wednesday night after officers approached him and two other men sitting in a 2006 Mercedes-Benz in this Los Angeles suburb and found a loaded firearm.
Lynch was arrested after officers determined the gun belonged to him. He was released that night on $35,000 bail.
Culver City police did not immediately return a phone message seeking information about why officers approached Lynch and his companions.
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.
A Bills spokesman had no comment.
The 22-year-old Lynch was the Bills' first-round draft pick out of California in 2007. He played in his first Pro Bowl earlier this month after being added to the team in place of injured Tennessee running back Chris Johnson.
Lynch's arrest marked the second time in less than a year that he has been in trouble with the law.
In June, Lynch pleaded guilty to a traffic violation and admitted speeding off in his Porsche Cayenne SUV after striking a female pedestrian near Buffalo's downtown bar district on May 31. The victim, a 27-year-old woman from suburban Toronto, was treated and released from the hospital later that day after sustaining a bruised hip and cut to her thigh that required seven stitches.
Lynch said it was raining hard when he saw a woman dancing in the street and slowed to let pass, then continued on his way. He said he was unaware he had hit anybody.
A judge ordered Lynch's driver's license revoked but the player appealed and was allowed to keep his license.