The contribution from thermally generated electron-positron pairs to the radiative losses from a black body is considered near the temperature corresponding to the electron's rest mass energy T-c = m(e)c(2)/k. The correction factors are defined as the ratio of corrected expressions (which also include the contribution from thermal pairs) to the classical expressions (which include merely photons). The correction factors for energy, free energy, and entropy fluxes have different values about 0.5T(c), while they have the same value at T much less than T-c and T much greater than T-c. The Stephan-Boltzmann's constant becomes temperature dependent due to the contribution of thermal pairs. According to the classical expressions of radiative losses, the ratio of energy flux to the absolute value of free energy flux is a constant and it is equal to 3. On the contrary, it is shown that it is a function of temperature about T-c and it has a maximum about 0.38T(c). The correction factor for mean energy per emitted thermal particle has also a maximum about T=0.42T(c).