The accused, Ravi, who used to iron the clothes in the locality, has been arrested, a police officer said.
According to police, Ravi allegedly took the six-year-old girl to lonely stretch in a park in Sector 19 and sexually abused her.
When some residents saw him, they nabbed the accused and took him to the office of a Samajwadi Party leader, who handed him over to police, said Station House Officer of Sector 20 police station, Amarnath Yadav.
An FIR has been lodged and accused Ravi has been arrested, he added.