  We report the discovery of a 4.5 um counterpart to the anomalous X-ray pulsar
(magnetar) 1E 2259+586 with the Spitzer Space Telescope. The mid-infrared flux
density is 6.3+/-1.0 uJy at 4.5 um and <20 uJy (at 95% confidence) at 8 um, or
0.02% of the 2-10 keV X-ray flux (corrected for extinction). Combining our
Spitzer measurements with previously published near-infrared data, we show that
the overall infrared emission from 1E 2259+586 is qualitatively similar to that
from the magnetar 4U 0142+61. Therefore the passive X-ray-heated dust disk
model originally developed for 4U 0142+61 might also apply to 1E 2259+586.
However, the IR data from this source can also be fitted by a simple power-law
spectrum as might be expected from magnetospheric emission.
