The magnetic structure of the entropy-stabilized oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O has been investigated using first-principles methods in combination with Monte Carlo (MC) simulations. Similar to other transition metal oxides with the rock salt structure, such as CoO and NiO, the dominant interaction in this entropic oxide is the antiferromagnetic (AFM) superexchange interaction that takes place between second nearest neighbor cations. This superexchange interaction is responsible for the long-range type-II antiferromagnetic order observed in the material, with ferromagnetic (111) planes coupled antiferromagnetically in the (111) direction. The Néel temperature (TN) is evaluated via MC simulation, where the entropic oxide is modeled by a lattice of randomly distributed strengths of magnetic exchanges obtained from the binary and ternary oxides. The composition dependence of TN suggests that the material becomes paramagnetic when the concentration of nonmagnetic species exceeds 84%. The comparison between the theoretical results and the available experimental data indicates that the magnetic interactions in the entropic oxide can be predicted from magnetic exchange parameters calculated in the binary and ternary oxides.