Akshay Ansurkar (19), Aniket Ansurkar (23) and Santikesh Rathod (18) were arrested for assaulting head-constable Ganpat Chavan, police said.
The incident took place near Sena Bhavan in Dadar at around 2.30 AM today.
The trio had got into an altercation with a taxi driver, and when Chavan, attached with Shivaji nagar police station, intervened, they beat him up, police said.
While the three fled from the spot on bikes after the incident, Chavan, who was taken to Nagpada police hospital, received six stitches near the left eye. He was discharged in the morning.