  A decay rate asymmetry of the top quark is discussed within the framework of
the supersymmetric standard model. Although new sources of CP violation in this
model are severely constrained from the electric dipole moments of the neutron
and the electron, there is a possibility that a top squark has a mass of around
100 GeV and CP violation in its interaction with a top quark is unsuppressed.
Then partial widths could be different between the decays $t\to bW^+$ and $\bar
t\to \bar bW^-$. The magnitude of this CP asymmetry can be of order $10^{-3}$,
which may be detectable in the near future.
