Beyonce just pulled off an AWESOME surprise at a Target in Harlem ... where she unexpectedly appeared at an event for the Boys & Girls Club ... and led an impromptu dance party!!!
Beyonce's choreographer was in the middle of conducting a dance lesson for the group ... when the pop star suddenly walked on stage ... AND THE WHOLE PLACE WENT NUTS!!
We're told Beyonce hung out for roughly 15 minutes -- and afterward, she bought a handful of her new CDs and handed them out to the group.
Check out the video -- the reactions are priceless!!