The optical conductivity sigma(omega,T) can be obtained with the same approximations employed in a previous work to calculate the static conductivity a(T) and magnetic susceptibility chi(T) of FeSi, a compound that behaves like a Kondo insulator with both quantities vanishing rapidly for T --> 0; the periodic Anderson model (PAM) for U --> infinity was employed to model FeSi, assuming that the system is in the intermediate valence region. The same treatment is employed in the present paper to describe the three properties for the same compound, and a fairly good agreement with the experimental results is obtained. The sum rule of sigma(omega,T), appropriate for the PAM, is well satisfied in the range of the experimentally measured temperatures. Some quantities derived from our results are of the same order of magnitude that was estimated from recent measurements of angle-resolved low-temperature photoemission in FeSi.621278827891