Rihanna and a female guest were grinding away on the dance floor, making the most of the time off.
Luckily Rihanna was appropriately dressed for the occasion in a skintight nude dress with cut out panels and sparkly tiara.
Kemp spent more than a month organizing the event.
Witnesses said guests sang Happy Birthday to the R&B star and Kemp presented her with a birthday cake decorated with copies of her tattoos.
The Rude Boy singer was also presented with a pile of presents at the party, in Phoenix, Arizona.
After her bash, Rihanna headed to Germany to do promotional activities for her new album.
European trip: After her birthday, Rihanna headed to Berlin yesterday, where she wowed fans in a little black dress and Christian Louboutin heels
Wow shelooking too good I really like it.