  Using 8.4 years of photometry from the AllWISE/NEOWISE multi-epoch catalogs,
we compare the mid-infrared variability properties of a sample of 2197 dwarf
galaxies (M_stellar < 2 x 10^9 h^-2 M_sun) to a sample of 6591 more massive
galaxies (M_stellar >= 10^10 h^-2 M_sun) matched in mid-infrared apparent
magnitude. We find only 2 dwarf galaxies with mid-infrared variability, a
factor of ~10 less frequent than the more massive galaxies (p = 6 x 10^-6),
consistent with previous findings of optical variability in low-mass and dwarf
galaxies using data with a similar baseline and cadence. Within the more
massive control galaxy population, we see no evidence for a stellar mass
dependence of mid-infrared variability, suggesting that this apparent reduction
in the frequency of variable objects occurs below a stellar mass of ~10^10 h^-2
M_sun. Compared to the more massive galaxies, AGNs selected in dwarf galaxies
using either their mid-infrared color or optical emission line classification
are systematically missed by variability selection. Our results suggest, in
agreement with previous optical studies at similar cadence, that variability
selection of AGNs in dwarf galaxies is ineffective unless higher-cadence data
is used.
