We study the effect of spatially dependent mass functions over the solution of the Klein-Gordon
equation in the (3+1)-dimensions for spinless bosonic particles where the mixed scalar-vector Coulomb-like
field potentials and masses are directly proportional and inversely proportional to the distance from the
force center. The exact bound-state energy eigenvalues and the corresponding wave functions of the KleinGordon
equation for mixed scalar-vector and pure scalar Coulomb-like field potentials are obtained by
means of the Nikiforov-Uvarov (NU) method. The energy spectrum is discussed for different scalar-vector
potential mixing cases and also for the constant-mass case.