The animal was seen behind a business in the 800 block of Portola Road by an off-duty Peninsula Humane Society/SPCA officer at about 6 p.m., according to the county Office of Emergency Services.
Sheriff's deputies went out looking for the cat but did not find it.
Mountain lions mostly avoid contact with humans, but residents are advised to be cautious and to avoid hiking or jogging at dawn, dusk and at night, when the cats are most active.
In the event of a mountain lion encounter, experts recommend facing the animal, making noise, throwing rocks or other objects and trying to appear as large as possible.
More mountain lion safety tips can be found on the state Department of Fish and Game's website at www.keepmewild.org.