The aim of the present study is to investigate the effect of the counter-rotating terms on the quantum dynamics of a harmonic oscillator in the presence of a deformed bath. We first obtain the Langevin equation of motion for damped oscillator with and without the rotating-wave approximation (RWA). Then, we study the effect of the counter-rotating terms on the diffusion coefficients. Then, we obtain the equation of motion for the harmonic oscillator correlation function with and without the RWA. Finally, we investigate the influence of the counter-rotating terms on the oscillator correlation function.