The structural and magnetic properties of Mg/Mn-doped ZnO were investigated by the first-principles study and Monte Carlo methods (MCs). Applying magnetic force theorem (MFT) and using Kohn-Sham orbitals in the GGA-PBE scheme, the exchange coupling parameters (J) were calculated to figure out the magnetic interactions between atomic sites. Mn-Mg volume clustered (C1) ferromagnetic (FM) state was preferred; herewith, the calculated magnetic moment of Mn was 4.19μB and Mg has the highest moment value when clustered with Mn ions. Nearest Mn ions interacted antiferromagnetic (AFM) despite the increasing distance lead them to be in FM. However, AFM/FM wasoriginated from the p-d hybridization, superexchange interaction and direct exchange between distant Mn ions. In addition, the Curie temperature (Tc) was calculated as 311K using averaged magnetization and magnetic susceptibility via MC.