  In massless QCD coupled to QED in an external magnetic field, a photon with
the linear polarization in the direction of the external magnetic field mixes
with the charge neutral pion through the triangle anomaly, leading to one
gapless mode with the quadratic dispersion relation $\omega \sim k^2$ and one
gapped mode. We show that this gapless mode can be interpreted as the so-called
type-B Nambu-Goldstone (NG) mode associated with the spontaneous breaking of
generalized global symmetries and that its presence is solely dictated by the
anomalous commutator in the symmetry algebra. We also argue a possible
realization of such nonrelativistic NG modes in 3-dimensional Dirac semimetals.
