TMZ spoke to police in Broadview Heights, Ohio ... who confirm Keyshia's nephew was arrested on December 2 in KC's Mercedes SUV. We're told during the arrest -- the suspect told cops, "I'm Keyshia Cole's nephew" .... but the cops weren't impressed and arrested him anyway.
Keyshia's car was immediately impounded and taken to a nearby lot -- where it remains under a foot of snow because she still hasn't picked it up.
Sources connected to the car tell us ... it's gonna take at least $700 -- plus court fees -- before Keyshia can free her whip.
Calls to Keyshia's reps were not immediately returned.