The present study investigates the second order excitation loads on the OC3 spar type Floating Offshore Wind Turbine (FOWT) subjected to nonlinear monochromatic Stokes second order waves in deep water. A theoretical methodology, originally developed for vertically axis-symmetric semi-submersible bodies is employed to derive the load Response Amplitude Operator (RAO). In addition, commercially available numerical tool AQWA which is based on potential flow theory, is used to model the hydrodynamic response. This numerical model incorporates Pinkster’s approximation to account for nonlinear diffraction loads. Furthermore, a Computational Fluid Dynamics (CFD) model has been developed using ANSYS Fluent to capture the detailed fluid dynamics in contrast to potential flow theory, which assumes the fluid as inviscid, irroration and incompressible. Although fluid viscosity is considered in the CFD model, the resulting RAOs are in good agreement with those obtained from both theoretical and numerical approaches. This agreement validates the CFD model and highlights its potential for future investigations into nonlinear effects for more complex geometries since the theoretical model is limited to vertically axis-symmetric bodies.