  We derive a semi-classical effective action and the kinetic equation for
massive Dirac fermions in electromagnetic fields. The non-Abelian Berry phase
structure emerges from two helicity states of massive fermions with positive
energy. The classical spin emerges as a vector in SU(2) helicity space. The
continuity equations for the fermion number and the classical spin are derived.
The fermion number is conserved while the spin charge is not conserved by
anomaly. Previous results about the coefficients of the chiral magnetic effect
for the fermion and axial currents in the chiral limit can be reproduced after
including the anti-fermion contributions. This provides an example for the
emerging spin and non-Abelian Berry phase of Dirac fermions arising from the
fermion mass.
