The incident took place around noon when the victim was going towards Madhu Vihar police station to join her duty.
The accused, identified as Ranjeet Kumar, a resident of Preet Vihar, was overpowered by fellow passengers and was beaten up before being handed over to the Madhu Vihar police.
A case of molestation was registered against Kumar and he was arrested, said a police officer.
The victim, the officer said, was in plain clothes while she was travelling in the bus.
Meanwhile, two more incidents of molestation were reported from the Capital on Wednesday.