According to witnesses cited by Fox News, the woman shot her boyfriend then herself. She was dressed in a headscarf and was an adult white female.
Four people have been taken to San Francisco hospital, but their conditions have not been revealed.
At a press conference shortly after the incident, San Mateo County Sheriff's Department confirmed the shooter was dead.
'At 12.46pm this afternoon, we received numerous 911 calls regarding gun shots at YouTube's campus.
'Police arrived at 12.48pm and immediately began a search for a possible shooter or shooters.
'Upon arrival, police encountered numerous employees fleeing. It was very chaotic.
'Officers encountered one gunshot victim...several minutes later while searching the building officers located a second gunshot wound victim that may have been self-inflicted.
'Two additional victims were located several minutes later at an adjacent business,' a spokesman said