  Variability of 226 AGNs in the near-infrared $J$, $H$, and $K'$ bands is
analyzed and discussed. An ensemble average for measured variabilities was
obtained for various samples of the AGNs divided by absolute $B$-magnitude
$M_B$, redshift $z$, and radio strength. All the samples in the $J$, $H$, and
$K'$ bands are found to give significant ensemble variability, but no
significant wavelength dependence is found. The ensemble variability in the
entire sample combining the $J$, $H$, and $K'$ samples is $\Delta m\approx
0.22$ mag, while $\Delta m\approx 0.18$ mag for the radio-quiet AGNs and
$\Delta m\approx 0.26$ mag for radio-loud AGNs. The ensemble variability for
the radio-quiet AGNs shows no significant $M_B$-dependence, while showing
positive $M_B$-dependence for the radio-loud AGNs. In any samples the measured
variability shows positive correlation among different passbands, with the
correlation coefficients of $r_{JH}$, $r_{HK'}$, and $r_{JK'}$ ranging from 0.6
to 0.9. For radio-quiet AGNs, the coefficient $r_{HK'}$ in a redshift range of
$0.1<z<0.3$ is significantly higher than $r_{JH}$ or $r_{JK'}$. The coefficient
for the radio-loud AGNs with $0.6<z<1.0$ is as high as 0.95, irrespective of
the passband. However, for the radio-quiet AGNs with $z>0.3$ and radio-loud
AGNs with $z<0.3$, we cannot confirm such strong correlation among different
passbands. All the features of near-infrared variability for the radio-quiet
AGNs are consistent with a simple dust reverberation model of the central
regions of AGNs. However, the features for the radio-loud AGNs are not fully
explained by such a model, and a non-thermal variable component is suggested as
a viable candidate for causing their large and fast variability in the
near-infrared region.
