The electrical resistivity and thermoelectric power as a function of temperature and Mn concentration for Ni0.6-t Mn (t) Zn0.4Fe2O4 (t = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) have been studied. It was observed that temperature variation of resistivity exhibits two breaks. Each break is associated with a change in activation energy. The activation energy in the paramagnetic region is found to be greater than that in the ferrimagnetic one. Moreover, it was found that the resistivity increases with increasing Mn content. The sign of thermoelectric power measurements revealed n-type conduction for all investigated samples. The results are explained according to the spin polaron model.