This paper highlights the behavior of steel-concrete composite beams strengthened by Basalt Fiber Reinforced Polymer (BFRP) composite tendons. A nonlinear finite element simulation was presented using ANSYS V15 program. The proposed model was verified by experimental data revealing that the FE predictions can be used with confidence to investigate various parameters that affect the behavior of externally strengthened steel-concrete composite beams. Using BFRP tendon for composite beams increased generally their ultimate capacity. A better performance of the composite beam can be obtained by increasing the pre-stressing level in tendon, by using a higher elastic modulus of the BFRP tendon and by increasing the tendon eccentricity. For higher composite action, the posttensioned Basalt FRP tendons enhanced the capacity of the composite beam. Using Basalt FRP tendon with a very low elastic modulus can prompt a risk of structural failure caused by premature fracture of the BFRP tendon.