Oakland police said no one else was hurt in the incident at the facility called San Antonio Neighborhood Health Center and that it was under investigation as a suicide, according to television station CBS San Francisco.
It was not immediately clear what might have motivated the man to kill himself.
The Alameda County Sheriff's Office in a message on Twitter said its bomb squad helped Oakland police ensure the area was safe.
CBS San Francisco reported that witnesses told police the man entered the Northern California clinic's lobby with what appeared to be a pipe bomb before he detonated the device.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)