The goal of this paper is to numerically investigate the effect of prestress on the propagation of elastic waves in straight and helical waveguides. The simulation technique, based on a semi-analytical finite element (SAFE) method, reduces the problem to the two-dimensional cross-section. The three-dimensional equilibrium equations of prestressed structures are written in the covariant and contravariant bases and used for the SAFE method. The eigenproblem can be solved by fixing the wavenumber and finding the angular frequency or inversely. Dispersion curves for single straight and helical wires will be computed to quantify the effect of prestress on the wave propagation.