  We compute the spin current rectification coefficient of a non-equilibrium
quantum dot subject to a spin bias and an {\it ac} charge bias with small
amplitude. As a function of the position of the resonant level the spin current
rectification coefficient shows a set of three peaks around the gate voltage at
which the resonant or the upper level of the dot is in the vicinity of the
equilibrium Fermi level in the leads. The peak heights can be related to the
average number of the quantum dot electrons. We discuss the frequency
dependence of the spin current rectification coefficient as well and emphasize
the effects of the photon-assisted spin transport through the dot.
