In order to understand the emergence and the influence of the "cage effect" in the dynamic response of a liquid, a detailed theoretical study of the frequency dependent friction of a Lennard-Jones liquid is carried out by using the mode coupling theory. The frequency dependent friction becomes increasingly bimodal in nature as the density of the liquid is increased beyond the liquid-solid coexistence line. The bimodality is most clearly manifested in the frequency dependence of the imaginary part of the friction. The mode coupling theory provides a nice physical interpretation of these results which are also in good agreement with the existing computer simulations.