  We investigate the effects of baryon chemical potential \mu on the shear
viscosity coefficient \eta and the viscosity to entropy density ratio \eta/s of
a pion-nucleon gas mixture. We find that \eta is an increasing function of T
and \mu, while the ratio \eta/s turns to a decreasing function in a wide region
of T-\mu plane. In the kinematical region we studied, the smallest value of
\eta/s is about 0.3.
