Mac Miller is not only livin' the dream ... he's stolen it from the '70s soul/funk band Aquarian Dream, which claims Mac ripped off the group's signature song.
According to the lawsuit ... the group's singer Jacques Burvick claims Miller stole the tune, "Yesterday (was so nice today)" from their album "Fantasy" and blatantly used the track for "Therapy," a song featured on Mac's album, "Faces."
Burvick says Miller's rep knew they were busted because when he called them out, they admitted they tried to contact him for the okay, but when they couldn't they did it anyway.
He says the song's been downloaded over 700,000 times from Mac's site OldJewish.com, among others ... and wants a judge to force Mac to dole out at least $150k in damages.
Time to face reality.