  We demonstrate that T invariance can be violated even when
Pontecorvo--Maki--Nakagawa--Sakata lepton mixing matrix is real. We obtain a
sufficient condition of T violation in neutrino oscillations in matter and
electromagnetic field. In the two-flavor model we derive the T-violating
spin-flavor transition probabilities. Then we prove that the transition
probabilities for neutrino in moving medium in electromagnetic field differ
from those for antineutrino in matter composed of antiparticles and
electromagnetic field only in the sign of the T-violating term.
