Magnetic properties of 6H-SiC doped with transition metal (TM) atoms are calculated using the density functional theory method (DFT). It is shown that TM doped in a 6H-SiC host may have both magnetic and nonmagnetic states. From the figures of their density of states (DOS) and partial density of states (PDOS) and to compare the energy differences between ferromagnetic and nonmagnetic states, we demonstrate that Cr and Mn-doped 6H-SiC emerge a half-metallic ferromagnetic state, Co and Ni-doped 6H-SiC create very little magnetic features, while Fe-doped 6H-SiC is in the nonmagnetic state. We also calculate the energy differences between ferromagnetic and antiferromagnetic of Cr, Mn and Fe-doped 6H-SiC in the doping concentration (8.34%). It is found that the energy of the antiferromagnetic state is lower than that of the ferromagnetic state.