Many materials used in industry show time and temperature dependant stress strain relationship. While essentially most of the materials exhibit stress relaxation or in general viscoelastic material properties, some of them are assumed as linear elastic to be able to make their stress calculations simpler. On the contrary, there are some materials showing intense viscoelastic stress strain relationship even at lower tem-peratures and short time periods. Most of these materials are employed in construc-tion industry as pavements on roads or bridges and needed a better understanding of their viscoelastic material properties and calculation methods for their design. For a better understanding and comparison between several material products in indus-try, their stress strain behavior shall be evaluated. Stress relaxation of materials, which shows time and temperature dependant properties, is investigated in this pa-per. For that reason first, relaxation test results existed in the literature are used to verify the numerical stress relaxation calculation of commercial FEM program, AN-SYS. Second, the determination of Prony series parameters and the commands to be entered in ANSYS to perform stress relaxation are given. Finally, the amount of error in the numerical calculation depending on time step sizes at different temperatures is presented.