  Using numerical simulations of cluster formation in the standard CDM model
(SCDM) and in a low-density, flat CDM model with a cosmological constant
(LCDM), we investigate the gravitational lensing explanation for the reported
associations between background quasars and foreground clusters. Under the
thin-lens approximation and the unaffected background hypothesis , we show that
the recently detected quasar overdensity around clusters of galaxies on scales
of $\sim10$ arcminutes cannot be interpreted as a result of the gravitational
lensing by cluster matter and/or by their environmental and projected matter
along the line of sight, which is consistent with the analytical result based
on the observed cluster and galaxy correlations (Wu, et al. 1996). It appears
very unlikely that uncertainties in the modeling of the gravitational lensing
can account for the disagreement between the theoretical predictions and the
observations. We conclude that either the detected signal of the quasar-cluster
associations is a statistical fluke or the associations are are generated by
mechanisms other than the magnification bias.
