Justin Bieber Headlines At Coachella for Audience of 10

Justin Bieber plus Coachella equals raging your face off ... is what you would think, but this video from inside a Coachella party is about to prove otherwise.

Sources at the dFm House tell us the Biebs showed up Friday afternoon with a small posse which included Vine star King Bach and headed straight for the piano.

We're told Justin's security asked everyone except a few of JB's buddies to clear a room in the estate. It's unclear what he performed because of the stereo blaring over his concerto ... still Bieber did his best piano man impression for about 20 minutes before heading out.

It's a long weekend and we're sure he will make plenty of time to rage his face off too.