The crash happened just after 6 p.m. Wednesday at the intersection of North Shoreline Boulevard and Plymouth Street, near the Google campus.
Witnesses tell ABC7 News several people rushed to help the motorcyclist, but he was unresponsive. Police have not yet identified him.
It's unclear if there were any employees on the bus at the time of the accident.
A Google spokeswoman issued a statement saying, "We are saddened to learn of this tragic incident. Our thoughts are with all those affected by this tragedy."
North Shoreline Boulevard has been reopened after it was closed for the investigation.