The teenager was at a shopping centre north of Malibu when the alleged assault is said to have happened.
The man, who hasn’t been named, claimed the attack happened while he was taking pictures of the 18-year-old.
Justin Bieber and his girlfriend Selena Gomez had left the building in Calabasas by the time officers arrived.
The man was taken to hospital for treatment and later released.
The Los Angeles County Sheriff’s Department wants anyone with information to contact them.
Spokeswoman Lillian Peck refused to give further details about the nature of the confrontation or any injuries suffered by the man.
Deputies are investigating the case as a misdemeanour battery complaint, a criminal offence in America involving unlawful physical contact.
Hollywood news website TMZ.com is reporting that the man behind the complaint is a professional celebrity photographer.
Citing accounts of witnesses at the scene, it said the man was blocking Justin Bieber’s car as the entertainer was trying to leave.
It claims a scuffle started after the star got out of his vehicle, asked the man to leave and the man refused.
There’s been no comment yet from the Canadian singer’s management.
Justin Bieber is due to release his third studio album, Believe, in June following the release of My World 2.0 in 2010 and Christmas record Under the Mistletoe last winter.