Passenger movements were restricted for a couple of hours after the bag was found, leading to a brief panic at the airport.
The black-coloured bag was first detected around 1 am by a CISF personnel in the arrival area of Terminal-3.
A bomb detection and disposal team, along with a dog squad, are at the spot. The airport premises is being sanitised.
Preliminary inputs suggest the content of the bag to be RDX. It was checked by an explosive detector and a dog. However, the exact nature of the explosive is being ascertained.
The explosive has been put under observation for the next 24 hours, only after which something certain about it could be said, they added.
It could be an explosive or an improvised explosive device (IED), but it is not clear at present.
The Delhi Police said a call was received around 1 am, following which the bag was found at arrival gate number two of the terminal.