Influence of externally forced initial flow conditions on axisymmetric cavity shear layer was studied. A sinusoidally heated strip upstream of the cavity excited Tollmien-Schlichting waves that, after amplification by the boundary layer, were introduced to the cavity shear layer. It is shown that by selecting a forcing frequency, which satisfies a phase difference criterion between two comers of the cavity and has an amplitude that is above the threshold amplitude, it is possible to excite a naturally nonoscillating shear layer. It is also shown that the frequency and amplitude of the oscillation in the self sustained mode can be controlled through external forcing. By using a feed-back control scheme, up to 40% reduction of the velocity fluctuation level can be obtained.