In this work, the thermal reservoir effects over the absorptive and dispersive nonlinear optical properties of a two-level molecular system in presence of classical electromagnetic fields, were modeled. The collective effects proper of the thermal reservoir are modeled as a time dependent frequency, whose manifestation is the broadening of the upper level according to a prescribed random function. Using the stochastic optical Bloch equations, analytical expression for the nonlinear induced susceptibilities and absorptive and dispersive optical properties, were obtained. Numerical calculations were carried out to construct surfaces corresponding to these optical properties as a function of the pump-probe frequency detuning, relationships between the longitudinal and transversal relaxation times, and molecular concentration of solute. Finally, we see an attenuation of these optical responses by the solvent effects and the high pump-intensity.