  We compute the force on a small neutral polarizable object moving at velocity
$\vec v$ relative to a photon gas equilibrated at a temperature $T$ We find a
drag force linear in $\vec v$. Its physical basis is identical to that in
recent formulations of the dissipative component of the Casimir force. We
estimate the strength of this universal Casimir drag force for different
dielectric response functions and comment on its relevance in various contexts.
