Senior Superintendent of Police Anoop T Mathew said the three girls, students of the same school, boarded the bus at Sakchi to go home when the men started teasing them.
The girls complained to the bus driver and the conductor and asked them to stop the bus, but their plea were ignored as the teasers were the driver's friends, the SSP said.
The girls then jumped from the running bus and one of them got injured, Mathew said.
Deputy Superintendent of Police Animesh Naithany said local people took the injured girl to MGM Hospital, where she was admitted.
It was not the usual bus in which they generally travel from Sakchi to Mango, the police informed.