Dielectric relaxation phenomena of 4-cyano-4'-n-alkyl-biphenyl (nCB; n=5 or 10) monolayers at the air-water interface have been investigated by measuring Maxwell displacement current (MDC; I)-area per molecule (A) isotherms and surface pressure (π)-A isotherms at several monolayer compression rates. It is found that I-A isotherms of 5CB monolayer clearly depend on molecular compression rates (α) in the range (range 2) where the surface pressure is almost zero, and that in contrast, I-A isotherms of 10CB monolayer fluctuate in range 2. These results indicate that the monolayer compression of 5CB in range 2 is a non-equilibrium process.