The fire broke out at the two-story building on the 9000 block of Rancho Real Road around 1:30 a.m.
It remains unclear if anyone was inside the unit where the fire began, but a couple and their two children were forced to evacuate.
Los Angeles County fire officials say the blaze was extinguished within 50 minutes.
No one was hurt, but two second-floor units were damaged.
Investigators are working to determine what caused the fire, but say it may have started in an enclosed carport under the units.