  We report on the nuclear X-ray properties of the radio galaxy NGC 6251
observed with XMM-Newton. NGC 6251 is a well-known radio galaxy with
intermediate FRI/II radio properties. It is optically classified as a Seyfert 2
and hosts a supermassive black hole with mass~6e8 solar masses. The 0.4-10 keV
EPIC pn continuum is best fitted by two thermal components (kT~0.5 and 1.4 keV,
respectively), plus a power law with photon index ~1.9 absorbed by a column
density NH~5e20 cm-2. We confirm the previous ASCA detection of a strong iron
line. The line, resolved in the EPIC pn spectrum, is adequately fitted with a
broad (sigma~0.6 keV) Gaussian at rest-frame energy 6.4 keV with EW 220 eV. We
also detect, for the first time, short-term, low-amplitude variability of the
nuclear flux on a timescale of a few ks. The spectral properties argue in favor
of the presence of a standard accretion disk, ruling out the base of the jet as
the sole origin of the X-rays. The moderate X-ray luminosity and lack of strong
intrinsic absorption suggest that NGC 6251 is a ``pure'' type 2 AGN which lacks
a broad-line region.
