In this paper, effect of an axial force and shaft characteristics on the lateral natural frequencies of a flexible rotating shaft with a cubic nonlinearity is investigated. Also this research performed for viscoelastic Voigt-Kelvin rotating shaft. The shaft is assumed to be uniform, and the Euler-Bernoulli theory is used to model the rotating shaft. Method of multiple scales is used to solve the dimensionless partial differential equation of the motion. Linear and nonlinear lateral natural frequencies are plotted for various shaft parameters and effects of these parameters and cubic nonlinearity is also discussed.