The 53-year-old actor and Amal were joined by some of their famous friends, including U2 frontman Bono, Cindy Crawford and her husband Rande Gerber at the low key bash taking place at a cafe in Malibu, reported E!Online.
Clooney looked relaxed and was dressed in a casual blue shirt with jeans. His human rights attorney fiance wore a green T-shirt with floral shorts.
"People got a show they didn't expect and other (restaurant patrons) said it was the best Mother's Day ever," a source said.