High temperature deformation behavior of Al0.2CoCrFeNiMo0.5 high entropy alloy was investigated in fully annealed condition. Microstructural studies were performed using SEM and EBSD, prior to testing, clearly shows a fully annealed microstructure consists of secondary sigma phase in the FCC matrix. Uniaxial tensile tests were performed in the temperature range of 25–900 °C at an initial strain rate of 10−3 s−1. Serrated plastic flow behavior was observed in the intermediate temperature range of 400–600 °C. The influence of the strain rate on the critical strain corresponding to the onset of serrations were studied which indicated that the serration behavior was type A and type C. Strain rate sensitivity close to zero, decrease in the elongation and microstructural investigations suggesting that dynamic strain aging (DSA) is the responsible mechanism for the serrated flow and that the Al solute interactions with dislocations might be the possible reason for DSA. Additionally, the fractography analysis clearly indicates that there is transition in the failure mode from the transgranular fracture to the intergranular fracture. © 2022 Elsevier B.V.