  If massive neutrinos are Majorana particles, then the lepton number should be
violated and neutrino-antineutrino oscillations will take place. In this talk,
we present the properties of CP violation in neutrino-antineutrino oscillations
with a non-unitary leptonic flavor mixing matrix, which naturally arises in the
type-I seesaw model due to the mixing between light and heavy Majorana
neutrinos. Taking into account current experimental bounds on the leptonic
unitarity violation, we show that the CP asymmetries induced by the non-unitary
mixing parameters can significantly deviate from those in the unitarity limit.
