CP Violation in the Heavy Neutrinos Production Process $e^+e^-\rightarrow N_1N_2$

The problem of CP conservation and CP violation for two heavy neutrinos production in $e^+e^-$ interaction is considered. Very convenient way of parametrization of the neutrino mass matrix, from which necessary and sufficient condition for CP conservation easily follows, is presented. Contrary to the Kobayashi-Maskawa mechanism, the effects of CP violation in the lepton sector with Majorana neutrinos can be very large. Change of the total cross section caused by CP violation can be much larger then the cross section itself.