Recently, Konyashin et al. [I. Konyashin, V. Khvostov, V. Babaev, M. Guseva, J. Mayer, A. Sirenko, A new hard allotropic form of carbon: Dream or reality International Journal of Refractory Metals and Hard Materials (article in press)] have reported electron energy loss spectra (EELS) of fcc. (fcc) carbon films that indicate unique electronic properties of this particular crystal phase of carbon. Motivated by that, we have investigated the optical properties of carbon in its fcc phase (Fm̅3m) by means of a first principles calcn. We present the calcd. dielec. tensor and EELS, which are in good agreement with the exptl. spectra. In the EELS of fcc carbon there exists only one peak located at 22-23 eV, we have reproduced this by the d. functional calcn. at 22 eV. The electronic d. of states and band structure is addnl. shown to get a deeper understanding of the optical response. In order to check the accuracy of our calcns. analogous results obtained for the diamond phase of carbon are included in this work.