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We analyze observations of the Seyfert galaxy NGC 4151 covering 90 years in the optical band and 27 years in the 2 -10 keV X-ray band. We compute the Normalized Power Spectrum Density (NPSD), the Structure Function (SF) and the Autocorrelation Function (ACF) for these data. The results show that the optical and X-ray variability properties are significantly different. X-ray variations are predominantly in the timescale range of 5 -1000 days. The optical variations have also a short timescaledoi:10.2172/813323 fatcat:amy3xulovzhnrehdauw6eqg6oq