LeRoy Police say Paul Kaiser, 26, of East Aurora was arrested.
He faces traffic and felony weapons charges.
Police say around 6:45am on Monday, they pulled over Kaiser along Lake Street Road.
They say he was speeding through the area.
Officers say when they smelled marijuana from the vehcile and asked to do a vehicle search.
When asked if there were any weapons in the vehicle, police say Kaiser cooperated and said that there were weapons in the trunk.
When the officer opened the trunk, police say a live grenade was found.
They say Kaiser said he bought the items online and had made them before.
The New York State Police Bomb Squad was called in to remove the grenade and safely detonate it.
A portion of the road was shut down for a short time and eight homes were evacuated.
The Erie County Sheriff's Department also issued a search warrant at his home in East Aurora due to a "public safety concern" to see if any further explosives were at that location.
The results of the search have not been released.
Along with the State Police and Erie County Sheriff's, the LeRoy Police Department was assisted by the LeRoy Fire Department, the LeRoy Ambulance, the Genesee County District Attorney's Office and the Federal Bureau of Alcohol, Tobacco and Firearms (ATF).