We observed two magnetars, 4U 0142+61 and 1E2259+568, with the Japanese infrared satellite AKARI to search for the time variability at wavelengths between 2-4 μm. We significantly detected 4U0142+61 in the 4μm band, and determined flux upper limits in the other two bands. We did not detect 1E 2259+586 in any of the bands, and determined upper limits. Comparing the detection of 4U 0142+61 in the 4μm band with the Spitzer observation from 2005, we found the flux was reduced to be 64%. We interpret this time variability in the infrared band as an increase of the inner radius of the dust disk around the neutron star, where the increase is due to the sublimation of the dust by the large flare of neutron star itself.