US website TMZ has claimed the singer became angry after he realised a fellow guest was filming a play-fight he was having with Disney star Kyle Massey, and asked for it to be deleted.
When they refused, Justin is said to have lashed out, and an eyewitness reported him to the police.
According to Sky News, the incident came after he was reportedly involved in a scuffle with two bartenders earlier on at the party, held at Serafina Sunset on Sunset Boulevard on Saturday (11 February).
The LA County Sheriff’s Department claimed to have received a battery report accusing Justin of assaulting all three men.
“The witness said he broke up the fights and asked Mr Bieber to leave. Mr Bieber refused to leave and remained at the restaurant,” police said.
“The witness stated, a few minutes later, he saw Mr Bieber arguing with a patron, when Mr Bieber suddenly headbutted the patron.”
While Sky News added no claims have yet been filed against Justin, TMZ also stated the investigation is still going ahead.
A spokesperson for the restaurant said: “We know very little about the alleged incident at Serafina Sunset with Justin Bieber.
“We always have pleasant experiences with Mr Bieber whenever he comes to Serafina.”