  Time evolution of shear viscosity $\eta$, entropy density $s$, and their
ratio $\eta / s$ in the central area of central gold-gold collisions at NICA
energy range is studied within the UrQMD transport model. The extracted values
of energy density, net baryon density and net strangeness density are used as
input to (i) statistical model of ideal hadron gas to define temperature,
baryo-chemical potential and strangeness chemical potential, and to (ii) UrQMD
box with periodic boundary conditions to study the relaxation process of highly
excited matter. During the relaxation stage, the shear viscosity is determined
in the framework of Green-Kubo approach. The procedure is performed for each of
20 time slices, corresponding to conditions in the central area of the fireball
at times from 1~fm/$c$ to 20~fm/$c$. For all tested energies the ratio $\eta /
s$ reaches minimum, $\left( \eta/s \right)_{min} \approx 0.3$ at $t \approx
5$~fm/$c$. Then it increases up to the late stages of the system evolution.
This rise is accompanied by the drop of both, temperature and strangeness
chemical potential, and increase of baryo-chemical potential.
