Officials said the incident was reported from the Nawada Metro station late last evening when the security personnel noticed on CCTV a girl crying at the stairs of the station.
She was immediately brought to the station controller's room as she was unable to give information about herself or her parents, they said.
Later, a woman identified as her mother Sunita M, came to the station looking for her lost daughter.
"Sunita said her daughter was playing in the vicinity of the station and reached there unknowingly. The girl was handed over to the mother after due verification by Central Industrial Security Force personnel," they said.