Jay Z and Beyonce -- Surprise Bitches ... We're at Coachella!

The first couple of hip hop made their mark on Coachella Saturday ... surprising two different audiences with unannounced appearances -- and the hipsters went BONKERS!

First up, Beyonce ... who danced her way onto the stage during little sister Solange's set. However Queen Bey didn't grace the Indio crowd with a single note.

Next, Jay Z ... who rapped alongside his former nemesis Nas for a few minutes -- then made his swift exit from the festival.