The unusual incident took place when a court clerk opened the box carrying the grenade.
At the time of explosion a judge was presiding over a high profile terror-case on Monday.
The grenade was among other explosives and weapons recovered from a suspect against which a case had been filed in the ATC for illegal possession of explosives.
The Bomb Disposal Squad (BDS) later reached the spot and was cleared the courtroom for any explosives. A probe has been ordered into the incident as properties produced in a court are usually disarmed by experts.
OneIndia News (With inputs from agency)