The arrest of James Smith, 35, on Wednesday came after Bangor police carried out a search warrant at a home on Essex Street Tuesday afternoon and found what they said was explosives inside.
Part of the street was shut down and some neighboring residents were evacuated as a precaution.
The Bangor Police Department's bomb squad moved in Tuesday night and removed the explosive material before everyone was allowed to return.
Smith is charged with criminal use of explosives and possession of a firearm by a prohibited person.
Police have not yet released any details about what the explosives were and what Smith allegedly was doing with them.