Temperature dependent magnetization of Ni0.5Co1.5MnSb quaternary Heusler alloy is investigated both theoretically (m-T) and experimentally (M-T). According to the XRD data, the crystal structure of Ni0.5Co1.5MnSb is compatible with the cubic crystal structure with space group symmetry Fm-3m and the lattice parameter of a = 5.968 angstrom. Experimental M-T curve is obtained at H = 1 T. The Curie temperature is obtained at about T-C(EXP) = 538.3 K. We also use effective field theory (EFT) developed by Kaneyoshi to model and investigate the m-T properties of Ni0.5Co1.5MnSb. We find that the theoretical m-T and experimental M-T results overlap at low temperatures (T < 100 K). Additionally, the Curie temperature of Ni0.5Co1.5MnSb is obtained at T-C(EFT) = 548.1 K and H = 0 T. The discrepancy between the theoretical and experimental value of T c is found to be 9.8 K only. One remarkable outcome of this study is that the central antimony (Sb3) atom has an important role when comparing the theoretical m-T and experimental M-T results of the Ni0.5Co1.5MnSb at high temperatures (T > 100 K). In particular, the theoretical m(Sb3)-T curve of the central Sb3 atom is much closer to the experimental M-T curve of Ni0.5Co1.5MnSb than that of the other components (m(Mn1), m(Mn2), m(Mn3), m(Sb1), m(Sb2), m(Ni) and m(Co)). Therefore, we strongly propose that one needs to pay close attention to the magnetization of the central atom especially in the lattice of Heusler alloys in both their predictive and experimental studies.