The crime was reported shortly after 10 p.m. near an Applebee's restaurant in the parking lot of the Encina Grande shopping center in the 1200 block of Broadway Plaza.
Three suspects approached the victim and one asked the man for his wallet and simulated having a pistol, police said.
The victim was able to walk away and alert authorities as the suspects fled the scene in a 1990s four-door Ford Taurus with tinted windows, police said. No one was injured.
Police say one of the suspects was a black man in his mid-30s who is about 5 feet 8 inches tall and has a goatee.
A second suspect is described as a black man in his mid-20s who is about 6 feet tall and weighs about 180 pounds, police said. No description is available of the third suspect. However, all three suspects were wearing all-black clothing, police said.
Anyone with information about the incident can contact the Walnut Creek Police Department at (925) 943-5844.