We report the discovery of a 6 month long mid-infrared transient, SDWFS-MT-1 (aka SN 2007va), in the Spitzer Deep, Wide-Field Survey of the NOAO Deep Wide-Field Survey Bo??tes field. The transient, located in a z = 0.19 low-luminosity (M[4.5] a??-18.6 mag, L/L* a?? 0.01) metal-poor (12 + log(O/H) a?? 7.8) irregular galaxy, peaked at a mid-infrared absolute magnitude of M[4.5] a??-24.2 in the 4.5 I?m Spitzer/IRAC band and emitted a total energy of at least 1051 erg. The optical emission was likely fainter than the mid-infrared, although our constraints on the optical emission are poor because the transient peaked when the source was behind the Sun. The Spitzer data are consistent with emission by a modified blackbody with a temperature of a??1350 K. We rule out a number of scenarios for the origin of the transient such as a Galactic star, active galactic nucleus activity, I?-ray burst, tidal disruption of a star by a black hole, and gravitational lensing.