  The recent measurement of the like-sign dimuon charge asymmetry in
semileptonic b-hadron decays by the D0 Collaboration is about 3 sigmas away
from the standard-model prediction, hinting at the presence of CP-violating new
physics in the mixing of B_s mesons. We consider the possibility that this
anomalous result arises from the contribution of a light spin-1 particle.
Taking into account various experimental constraints, we find that the effect
of such a particle with mass below the b-quark mass can yield a prediction
consistent with the anomalous D0 measurement within its one-sigma range.
