In this paper, we propose a method for estimating the frequency modulation of EEGs based on Fourier filtering of the initial signal on a narrow frequency band, followed by calculation of the time taken to reach both maximum and minimum peak values of the reconstructed signal (peak-to-peak periods). The resulting sequences were processed using the Fourier transform. EEGs recorded from healthy volunteers during photostimulation were used as the objects of study. Overall, EEG responses with a frequency range of 7 to 9 Hz demonstrated a more pronounced phenomenon of frequency modulation for occipital leads than those with the frequency range of 13 to 15 Hz. There were almost no differences in power spectral indices that modulate EEGs. Two types of EEG frequency modulation were revealed in the studied frequency ranges; the first type is not related to frequencies and is characterized by either a high or low level of exposure, while the second type has a connection between the nature of the modulation and the “carrier” frequency of the signal.