  In the framework of phenomenological model we consider dynamics of a
compensated collinear antiferromagnet (AFM) in the presence of spin-polarised
current. The model is based on the assumption that AFM spins are localised and
spin torque is transferred to each magnetic sublattice independently. It is
shown that in AFM spin current i) can be a source of the "negative friction";
and ii) modifies spin-wave frequencies. Equilibrium state of AFM can be
destabilized by the current polarized in parallel to AFM vector. Threshold
current at which the loss of stability takes place depends upon the magnetic
anisotropy of AFM.
