  We present an extensive analysis of the late-time mid-infrared (mid-IR)
evolution of Type IIb SN 1993J from 10 up to 26 years post-explosion based on
archival $-$ mostly previously unpublished $-$ photometric data of Spitzer
Space Telescope in conjunction with an archival IRS spectrum. SN 1993J is one
of the best-studied supernovae (SNe) with an extensive, decade-long
multi-wavelength dataset published in various papers; however, its detailed
late-time mid-IR analysis is still missing from the literature. Mid-IR data
follows not just the continuously cooling SN ejecta but also late-time dust
formation and circumstellar interaction processes. We provide evidence that the
observed late-time mid-IR excess of SN 1993J can be described by the presence
of two-component local dust with a dust mass of $\sim(3.5-6.0)\times 10^{-3}
M_{\odot}$ in case of a partly silicate-based dust composition. Source of these
components can be either newly-formed dust grains, or heating of pre-existing
dust via ongoing CSM interaction detected also at other wavelengths. If it is
newly-formed, dust is assumed to be located both in the unshocked inner ejecta
and in the outer cold dense shell, just as found in the Cassiopeia A remnant
and also assumed in other dust-forming SNe in a few years after explosion.
