According to law enforcement, the actor was arrested around 4 AM Sunday in Manhattan Beach, CA -- about 30 minutes south of Los Angeles.
We're told Vaughn is still in custody right now. The details of his arrest are still unclear, but according to a source ... he was stopped at a checkpoint while driving with a passenger in his car.
If charged, this would be Vaughn's first DUI offense.
We've reached out to his reps ... no word back yet.