  We present mean-field and quantum Monte Carlo results that suggest the
existence of an itinerant antiferromagnetic ground state in the half-filled
$U-t-t'$ model in two dimensions. In particular, working at $t'/t=-0.2$ we
found that antiferromagnetic long range order develops at $U_{c_1}/t\approx
2.5$, while a study of the density of states $N(\omega)$ and the response to an
external magnetic field indicates that the system becomes insulating at a
larger coupling $4<U_{c_2}/t<6$.
