Plainclothes detectives spotted a group of people gathered around two suspicious vehicles in the west parking lot of Mission Plaza at state Highway 12 and Mission Boulevard around 11 p.m., police said.
Patrol officers responded at the request of the detectives and contacted the group, according to police.
The officers learned the people were East Bay residents and several were on parole or were ex-felons. Police also allegedly located a loaded sawed off shotgun in one of the vehicles.
The six suspects, ages 29 to 34, were arrested on various charges including being a felon in possession of a handgun and carrying a concealed firearm, police said.