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Recently, a class of Dirac semimetals, such as Na3Bi and Cd2As3, are discovered to carry Z2 monopole charges. We present an experimental mechanism to realize the Z2 anomaly in regard to the Z2 topological charges, and propose to probe it by magnetotransport measurement. In analogy to the chiral anomaly in a Weyl semimetal, the acceleration of electrons by a spin bias along the magnetic field can create a Z2 charge imbalance between the Dirac points, the relaxation of which contributes a measurable positive longitudinal spin magnetoconductivity (LSMC) to the system. The Z2 anomaly induced LSMC is a spin version of the longitudinal magnetoconductivity (LMC) due to the chiral anomaly, which possesses all characters of the chiral anomaly induced LMC. While the chiral anomaly in the topological Dirac semimetal is very sensitive to local magnetic impurities, the Z2 anomaly is found to be immune to local magnetic disorder. It is further demonstrated that the quadratic or linear field dependence of the positive LMC is not unique to the chiral anomaly. Base on this, we argue that the periodic-in-1/B quantum oscillations superposed on the positive LSMC can serve as a fingerprint of the Z2 anomaly in topological Dirac semimetals.

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