Ghaleb Awali, 40, was "an official of the resistance," the spokesman said. He declined to give any details and spoke on condition of anonymity.
Al-Manar TV, affiliated with Hezbollah, showed pictures of the burned out car and said it blew up when "one of the strugglers in the resistance" started the engine to leave his home.
A Lebanese security official said the blast went off in the predominantly Shiite Muslim neighborhood of Harat Hreik, a Hezbollah stronghold.
Hezbollah said in a statement that Awali died instantly, though a Lebanese security official said he was rushed to a nearby Hezbollah-run hospital where he died soon after.