The flight had originated from Imphal.
A police official said that a lady, who boarded the plane from Guwahati, delivered a pre-mature baby during the journey. The suspect was identified after all female passengers onboard were questioned.
She was held back by the police for further investigation.
The airline, in a statement, said that the new-born infant was found lifeless and abandoned in one of the lavatories when the aircraft was being prepared for landing.
"The police were alerted and a doctor from the medical team at the Delhi International Airport confirmed that the baby had been delivered onboard."
The matter has been reported to the Directorate General of Civil Aviation (DGCA) and the airline's staff are attending to other guests and cooperating with the Delhi Police.
"We will be assisting in the investigation and cooperating with all concerned agencies," the statement said.