The district police acted swiftly and arrested constable Rajinder Singh, who is posted in Kot Bhalwal central jail, a police officer said.
The girl was on her way home in a mini bus when Singh allegedly molested her, police said, adding that when a group of students objected, he chased them out of the vehicle.
As the news spread, people in hundreds assembled in Bari Barahamana chowk and blocked highway.
Later, police rushed to the spot in Bari-Barahamana area and arrested the cop and registered a case against him.
The investigation is going on, police said.