  Magnetic field effect on linear and nonlinear conductivity in a
quasi-one-dimensional Weyl semimetal with a charge density wave (CDW)
(TaSe$_4$)$_2$I is studied. Longitudinal magnetoresistance in all known regimes
of CDW motion (linear conduction, creep, sliding, "Fr\"ohlich
superconductivity") is small, positive and do not exceed a fraction of per
cent. Similar magnetotransport measurements were performed in samples profiled
by focused ion beams is such a way that motion of the CDW in them is
accompanied by phase slip of the CDW. In such samples, a peak-like
non-parabolic negative magnetoresistance is observed in relatively small
magnetic fields $B \lesssim 4$ T in the nonlinear conduction regime in both
longitudinal and transverse geometries. Our results differ significantly from
ones obtained earlier and raise the question concerning conditions for
observing the axion anomaly in Weyl semimetals in the Peierls state.
