  We study a new scenario for baryogenesis due to the spontaneous breaking of
the $CPT$ invariance through the interaction between a baryon current and a
hypermagnetic helicity. The hypermagnetic helicity (Chern-Simons number) of
$U(1)_Y$ provides a $CPT$ violation background for the generation of baryons
via sphaleron processes, which protects these baryons from the sphaleron
wash-out effect in thermal equilibrium. It is shown that if the present
amplitude of the resultant magnetic fields are sufficiently large, for a wide
range mass scale (from TeV to the Planck scale), the observational magnitude of
the baryon asymmetry of the Universe can be realized.
