We investigated the electronic structures of antiferromagnetic (AFM) CeNMSb2 (NM = Cu and Au) by using the full-potential linearized-augmented-plane-wave method to clarify the role of 4f electrons in determining the ground state. Total-energy differences show that it is necessary to include both spin-orbit coupling (SOC) and the so-called LDA + U method in the spin-polarized calculation to predict the correct magnetic easy axis for AFM CeNMSb2 compounds. The spin density, density of states and SOC energy calculated by using 1.s matrix elements of f-orbitals indicate that the effects of SOC of Ce atom, especially the Ce 4f electrons, play a crucial role to determine the magnetic easy axes of these systems. The on-site Coulomb interaction of Ce atom is also very important. (C) 2016 Elsevier B.V. All rights reserved.