Electroweak contribution to the top quark forward-backward asymmetry at the Tevatron

The electroweak contributions to the forward-backward asymmetry in the production of top-quark pairs at the Tevatron are evaluated at O(alpha(2)) and O(alpha alpha(2)(s)). We perform a detailed analysis of all partonic channels that produce an asymmetry and combine them with the QCD contributions. They provide a non-negligible addition to the QCD-induced asymmetry with the same overall sign, thus enlarging the standard model prediction and diminishing the observed deviation. For the observed mass-dependent forward-backward asymmetry a 3 sigma deviation still remains at an invariant-mass cut of M-t (t) over bar > 450 GeV.