  The complete next-to-next-to-leading order (i.e. $O(v^2)$, $O(v \alpha_s)$
and $O(\alpha_s^2)$) relativistic corrections to the total photon mediated
$t\bar t$ production cross section at threshold are presented in the framework
of nonrelativistic quantum chromodynamics. The results are obtained using
semi-analytic methods and ``direct matching''. The size of the
next-to-next-to-leading order relativistic corrections is found to be
comparable to the size of the next-to-leading order ones.
