  The $CP$ violation in the neutrino transition electromagnetic dipole moment
is discussed in the context of the Standard Model with an arbitrary number of
right-handed singlet neutrinos. A full one-loop calculation of the neutrino
electromagnetic form factors is performed in the Feynman gauge. A non-zero $CP$
asymmetry is generated by a required threshold condition for the neutrino
masses along with non-vanishing $CP$ violating phases in the lepton flavour
mixing matrix. We follow the paradiagm of $CP$ violation in neutrino
oscillations to parametrise the flavour mixing contribution into a series of
Jarlskog-like parameters. This formalism is then applied to a minimal seesaw
model with two heavy right-handed neutrinos denoted $N_1$ and $N_2$. We observe
that the $CP$ asymmetries for decays into light neutrinos $N\to \nu\gamma$ are
extremely suppressed, maximally around $10^{-17}$. However the $CP$ asymmetry
for $N_2 \to N_1 \gamma$ can reach of order unity. Even if the Dirac $CP$ phase
$\delta$ is the only source of $CP$ violation, a large $CP$ asymmetry around
$10^{-5}$-$10^{-3}$ is comfortably achieved.
