  We report the study of the helicity driven photocurrents in graphene excited
by mid-infrared light of a CO$_2$-laser. Illuminating an unbiased monolayer
sheet of graphene with circularly polarized radiation generates -- under
oblique incidence -- an electric current perpendicular to the plane of
incidence, whose sign is reversed by switching the radiation helicity. We show
that the current is caused by the interplay of the circular $ac$ Hall effect
and the circular photogalvanic effect. Studying the frequency dependence of the
current in graphene layers grown on the SiC substrate we observe that the
current exhibits a resonance at frequencies matching the longitudinal optical
phonon in SiC.
