  We report the thermoelectric transport properties in the orbital-ordered Mott
insulating phase of Ca$_2$RuO$_4$ close to and far from equilibrium. Near
equilibrium conditions where the temperature gradient is only applied to the
sample, an insulating but non-monotonic temperature variation of the Seebeck
coefficient is observed, which is accounted for in terms of a
temperature-induced suppression of the orbital order. In non-equilibrium
conditions where we have applied high electrical currents, we find that the
Seebeck coefficient is anomalously increased in magnitude with increasing
external current. The present result clearly demonstrates a non-thermal effect
since the heating simply causes a decrease of the Seebeck coefficient, implying
a non-trivial non-equilibrium effect such as a modification of the spin and
orbital state in currents.
