Аннотация:The periodicity P0 = 160.0101±0.0001 min in brightness variations of active galactic nuclei is questioned by some astrophysicists. Extensive photometric observations of the Seyfert galaxy NGC 4151 were made with two reflectors at the Crimean Observatory in an effort to verify the existence of the P0-effect. The new data confirmed the presence of the P0-periodicity with a phase stable over 26 years and a mean harmonic amplitude of 0.007m in the V band. This result is also substantiated by an analysis of the X-ray observations from the Ariel-5, EXOSAT, and Ginga satellites (1975 - 1991). Since the same period was found in the power spectrum of global oscillations of the Sun, the authors infer that it is of cosmological origin.