  We have obtained optical multicolour (UBVRI) linear polarimetric data for 46
of the brightest stars in the area of the open cluster NGC 6124 in order to
investigate the properties of the interstellar medium (ISM) that lies along the
line of sight toward the cluster. Our data yield a mean polarization efficiency
of $P_V/E_{B-V}=3.1\pm$0.62, i.e., a value lower than the polarization produced
by the ISM with normal efficiency for an average color excess of $E_{B-V}=0.80$
as that found for NGC 6124. Besides, the polarization shows an orientation of
$\theta \sim 8^\circ$.1 which is not parallel to the Galactic Disk,an effect
that we think may be caused by the Lupus Cloud. Our analysis also indicates
that the observed visual extinction in NGC 6124 is caused by the presence of
three different absorption sheets located between the Sun and NGC 6124. The
values of the internal dispersion of the polarization ($\Delta P_V\sim 1.3% $)
and of the colour excess ($\Delta E_{B-V}\sim 0.29$ mag) for the members of NGC
6124 seem to be compatible with the presence of an intra-cluster dust
component. Only six stars exhibit some evidence of intrinsic polarization.Our
work also shows that polarimetry provides an excellent tool to distinguish
between member and non-member stars of a cluster.
