Only if really all the mass of the antimatter is usable energy for propulsion. A large chunk this energy would probably be in the form of gamma ray photons: they are not usable for thrust and irradiate the materials of the spaceship, another large chunk would be heat. And I assume you would also need quite a bit of energy for whatever vessel is holding the antimatter in place (magnetic fields maybe?), to avoid that the entirety of the 10^14J is produced instantly by annihilation with normal matter.