The crime occurred about 1:35 a.m. in the 5700 block of Sepulveda Boulevard, the Culver City Police Department reported.
"The victim had just withdrawn money from the ATM when he was approached by the suspect, who produced a black handgun and demanded his cash," police said in a statement.
"After taking the money, the suspect ran towards Sprouts Market and out of view," police said.
The suspect, who fled with $400, was described as about 20 years old, 6 feet tall and with a thin build. He was wearing a surgical mask, a gray hooded sweatshirt and dark pants.