  We report the discovery of excess 4.5 and 8 micron emission from three
quiescent black hole low-mass X-ray binaries, A 0620-00, GS 2023+338, and XTE
J1118+480. The mid-infrared emission from GS 2023+338 probably originates in
the accretion disk. However, the excess emission from A 0620-00 and XTE
J1118+480 is brighter and peaks at longer wavelengths, and so probably
originates from circumbinary dust that is heated by the light of the secondary
star. We find that the inner edge of the dust distribution lies near 1.7 times
the binary separation, which is the minimum radius at which a circumbinary disk
would be stable against tidal disruption. The excess infrared emission is not
detected at 24 micron, which implies that the dust does not extend beyond about
3 times the binary separation. The total masses of circumbinary material are
between 10^22 and 10^24 g. The material could be the remains of fall-back disks
produced in supernovae, or material from the companions injected into
circumbinary orbits during mass transfer.
