  We consider a baryogenesis scenario via the oscillation of right-handed
neutrinos with Majorana masses of the order of GeV, which are also responsible
for neutrino masses by the seesaw mechanism. We study how the initial condition
alters the prediction of the present baryon asymmetry by this mechanism. It is
usually assumed that the abundance of right-handed neutrinos is zero after the
reheating of the inflationary universe and they are produced in scattering
processes by the renomalizable Yukawa interaction. However, the
higher-dimensional operator with right-handed neutrinos may provide an
additional production which is most effective at the reheating epoch. It is
shown that such an initial abundance of right-handed neutrinos can
significantly modify the prediction when the strong washout of the asymmetry is
absent. This leads to the parameter space of the model for the successful
baryogenesis being enlarged.
