The hand grenade was found wrapped in a polythene bag near the family court around 9.40 AM, Senior Superintendent of Police Akash Kulhari said.
The entire area was vacated and a search operation was being carried out by police and bomb squad personnel.
The hand grenade has been defused, he said.
Searches were also being carried out near ghats along the Ganga river and other religious sites in the area, the police officer said.