  We present a possible explanation of the recently observed 511 keV
$\gamma$-ray anomaly with a new ``millicharged'' fermion. The new fermion is
light (${\cal O}({\rm MeV})$) but has never been observed by any collider
experiments mainly because of its tiny electromagnetic charge $\epsilon e$. We
show that constraints from its relic density in the Universe and collider
experiments allow a parameter range such that the 511 keV cosmic $\gamma$-ray
emission from the galactic bulge may be due to positron production from this
millicharged fermion.
