  We determine the nuclear spectral energy distribution (SED) from the radio to
the gamma-ray band for the FR I radio galaxy NGC6251, by using both data from
the literature and analyzing HST and X-ray archival data. In the Log nu - Log
nu F(nu) representation, the SED has two broad peaks, and it is remarkably
similar to those of blazars. We show that the low-energy peak can be explained
in terms of synchrotron radiation, while the high energy peak is most plausibly
produced by inverse Compton scattering. This brings direct support to the FR
I-BL Lacs unification model. We model the overall emission in the frame of a
synchrotron self-Compton scenario, which well describes the SED of BL Lacs. The
model parameters we obtain confirm also quantitatively the FR I-BL Lac
unification model and imply a rather small viewing angle to this source (theta
<~ 20deg). NGC6251 is the second radio galaxy, in addition to Centaurus A, for
which a similar analysis has been performed. A significant improvement with
respect to the case of Cen A is the absence of obscuration in NGC6251, which
strengthens the overall result.
