The oxidation/thermal stabilization of polyacrylnitrile (PAN) precursor fibers is a highly exothermic and time-consuming process. In several reports, the reduction of thermal stabilization time was shown for an irradiation of PAN at room temperature in different atmospheres. Since electron induced chemical reactions strongly depends on the polymer chain segment mobility, the present investigation reports the electron treatment of PAN homopolymer and copolymer powder in air and nitrogen atmosphere at an average temperature of 130 °C for the first time. This irradiation temperature was precisely selected in order to study the electron induced changes at temperatures above the glass transition temperature, but below the initiation temperature of thermal induced cyclization. The average dose rate of all electron beam (EB) treatments amounted to 0.77 kGy/s in order to keep the temperature fluctuation within the range of ± 5 K. In addition, several analyses were done in order to characterize the type of radicals, the crosslinking behavior, the functional groups, the exothermic behavior as well as the thermal stability of virgin and EB modified powder samples. Based on the calculated values of extent and degree of cyclization some correlations between functionalization and crosslinking were drawn with respect to cyclization and maximum residual mass at 800 °C.