  We present a group-galaxy cross-correlation analysis using a group catalog
produced from the 16,500 spectra from the optical zCOSMOS galaxy survey. Our
aim is to perform a consistency test in the redshift range 0.2 < z < 0.8
between the clustering strength of the groups and mass estimates that are based
on the richness of the groups. We measure the linear bias of the groups by
means of a group-galaxy cross-correlation analysis and convert it into mass
using the bias-mass relation for a given cosmology, checking the systematic
errors using realistic group and galaxy mock catalogs. The measured bias for
the zCOSMOS groups increases with group richness as expected by the theory of
cosmic structure formation and yields masses that are reasonably consistent
with the masses estimated from the richness directly, considering the scatter
that is obtained from the 24 mock catalogs. An exception are the richest groups
at high redshift (estimated to be more massive than 10^13.5 M_sun), for which
the measured bias is significantly larger than for any of the 24 mock catalogs
(corresponding to a 3-sigma effect), which is attributed to the extremely large
structure that is present in the COSMOS field at z ~ 0.7. Our results are in
general agreement with previous studies that reported unusually strong
clustering in the COSMOS field.
