The victim was the daughter of a woman with whom he was in a live-in relationship.
The sub-inspector, identified as Sajjan Kumar Chauhan, was arrested on Monday's morning and suspended.
The incident took place on Sunday's night when Sajjan was drunk. After consuming alcohol, the policeman had a brawl with victim's mother and then allegedly molested the girl when she was sleeping.
After the incident, the girl approached police which registered a case against Sajjan.
"We have arrested Sajjan and charged him under the Protection of Children from Sexual Offences and other Sections of IPC," said a police officer.