47-year-old Cody Charles Johnson was arrested at his home in Garden Grove on Wednesday.
Johnson is suspected of molesting the girl about 20 times.
The alleged victim, who is now 25, contacted police when she learned that Johnson still had a job around children, Orange County Sheriff's Department spokesman Jim Amormino said.
Johnson has worked for the Garden Grove Unified School District for 14 years.
He worked as a food service employee from 1997 to 2005.
In 2005, he began working as a school bus driver.
Johnson has been a bus driver for special needs children for the past six years, according to Amormino.
Authorities believe there may be additional victims, and they're asking anyone with information to come forward.
Johnson is currently being held on $100,000 bail.
Johnson was booked on suspicion of continuous sexual abuse of a child. He was being held in lieu of $100,000 bail.