  We study critical phenomena of nonequilibrium phase transitions by using the
AdS/CFT correspondence. Our system consists of charged particles interacting
with a heat bath of neutral gauge particles. The system is in current-driven
nonequilibrium steady state, and the nonequilibrium phase transition is
associated with nonlinear electric conductivity. We define a susceptibility as
a response of the system to the current variation. We further define a critical
exponent from the power-law divergence of the susceptibility. We find that the
critical exponent and the critical amplitude ratio of the susceptibility agree
with those of the Landau theory of equilibrium phase transitions, if we
identify the current as the external field in the Landau theory.
