Alkali-activated slag/fly ash (AASF) concrete can be used as an environmentally friendly replacement to ordinary portland cement concrete (OPC). However, the development of microcracks inAASF concrete is mainly due to high brittleness, which causes negative impacts on its engineering properties. This study investigates the effect of the addition of non-metallic fibers including polypropylene fiber (PF) and glass fiber (GF) on the engineering properties of ambient-cured AASF concrete. The investigated engineering properties of AASF concrete include workability, compressive strength, splitting tensile strength, direct tensile strength, flexural strength, and stress-strain behavior under axial compression. It was found that the engineering properties of ambient-cured AASF concrete improved significantly with the addition of GF compared to the addition of PF. However, the workability of AASF concrete decreased with the addition of PF and GF. Overall, the ductility of ambient-cured AASF concrete increased significantly with the addition of PF and GF.