Actor Anton Yelchin, known for his roles in "Star Trek" and "Alpha Dog," was killed early Sunday morning after getting pinned by his own car ... TMZ has learned.

Yelchin's friends became alarmed because he was supposed to meet them hours earlier for a rehearsal. They went to his San Fernando Valley home at around 1 AM and found him pinned between his car and a brick mailbox pillar, which was attached to a security gate.

Law enforcement tells us the engine was running when his body was discovered, and the car was in neutral. The driveway was on a fairly steep incline. It's unclear why he got out of the car.

Cops do not suspect foul play.

Yelchin was 27.