  We study the ac anomalous Hall conductivity $\sigma_{xy}(\omega)$ of a Weyl
semimetal with broken time-reversal symmetry. Even in the absence of free
carriers these materials exhibit a "universal" anomalous Hall response
determined solely by the locations of the Weyl nodes. We show that the free
carriers, which are generically present in an undoped Weyl semimetal, give an
additional contribution to the ac Hall conductivity. We elucidate the physical
mechanism of the effect and develop a microscopic theory of the free carrier
contribution to $\sigma_{xy}(\omega)$. The latter can be expressed in terms of
a small number of parameters (the electron velocity matrix, the Fermi energy
$\mu$, and the "tilt" of the Weyl cone). The resulting $\sigma_{xy}(\omega)$
has resonant features at $\omega \sim 2 \mu$ which may be used to separate the
free carrier response from the filled-band response using, for example, Kerr
effect measurements. This may serve as diagnostic tool to characterize the
doping of individual valleys.
