Steady state flow behavior of the FeCoNiCrMn high-entropy alloy at temperatures ranging from 1023 to 1123 K was systematically characterized. It was found that the stress exponent (i.e., the reciprocal of strain-rate sensitivity) was dependent on the applied strain rate, and specifically the stress exponent is high (∼5) in the high strain rate regime, but decreases with decreasing strain rate. Microstructural examinations of the samples before and after deformation were performed to understand the interplay of the microstructures with the corresponding properties. Based on the observations, it was proposed that, at high strain rates, the deformation of the current high-entropy alloy was controlled by dislocation climb and the rate limiting process was the diffusion of Ni. At low strain rates, however, the deformation appeared to be controlled by the viscous glide of dislocations. Moreover, at the slowest strain rate (i.e., the longest thermal exposure time), new phases evolved, which caused elemental redistribution and weakening of the material.