A Boston police officer is facing charges after authorities say he assaulted a woman during a domestic altercation.

Middlesex District Attorney Marian Ryan's office says Officer Patrick McCarthy pleaded not guilty Wednesday in Lowell District Court to charges of assault and battery on a household member.

Prosecutors say a woman told Tewksbury police on Tuesday night that the 35-year-old officer threatened to push her down a staircase, slapped her and threw her to the ground. The nature of McCarthy's relationship with the woman is unclear.

A Boston Police Department spokesman says McCarthy is on paid leave pending the outcome of the case.

His lawyer declined The Boston Globe's request for comment. He is due back in court on Sept. 29.