The incident is alleged to have taken place in Ottawa, Canada, at a venue where Bieber was playing a gig.
TMZ reports that a female employee of the venue filed a police report claiming that Bieber, or one of his entourage, hit her with an object.
It is alleged that the object was a foam projectile from a Nerf gun. Reportedly, Bieber was playing with the toys with his 3-year-old brother and 4-year-old sister, and one of the 'darts' hit the woman.
The Ottowan police are taking the claim seriously and have been interviewing people at the venue.
Bieber has been subject to a number of claims, allegations and lawsuits recently, including allegations he slept with Rihanna, Ke$ha and Penelope Cruz, being forced to take a paternity test to refute claims he had fathered a child, and a $9m lawsuit from a woman who argues he made a crowd at one of his concerts dangerously loud, and subsequently damaged her hearing.
Bieber's acoustic album Believe Acoustic is released on January 29. The album features reworked material from his previous studio album.
Watch Bieber perform 'As Long As You Love Me' from Believe Acoustic below: