Is antimatter matter?
No. Antimatter is the direct opposite of matter: the antimatter equivalent of electrons are positrons (electrons with a positive charge) and the antimatter equivalent of a proton is an antiproton (negative charge). Neutrons and antineutrons, being neutral are different not in charge, but in magnetism: antineutrons have the opposite magnetic moment (magnetic moment is another electromagnetic property). Antimatter is the opposite of matter.