  We present preliminary results of a 25 ks XMM-Newton observation of the
largest sample of Extremely Red Objects (EROs) available to date (about 450
sources), selected in a contiguous area of 700 arcmin^2 (Daddi et al. 2000).
Five of the 36 hard X-ray selected sources brighter than 7x10^{-15} erg cm^{-2}
s^{-1} in the 2-10 keV band are associated with EROs. All of the X-ray detected
EROs show rather extreme X-ray-to-optical flux ratios, suggesting the presence
of highly obscured AGN activity.
