For the star BO Cep, an anomalous color variability is revealed in addition to the usual variability typical for rapid irregular variables with Algol-like minima. Contrary to all the stars of this type, at maximum light the color index B-V for the star BO Cep decreases as the magnitude V increases. The lack of the correlation between the color index U-B and the magnitude V as well as different dependences of the color indices B-V and V-R on the magnitude V which are opposite in sign imply that the color abnormality is caused by an unidentified additional radiation manifesting itself in the photometric band B. Some suggestions on a possible role of the star BO Cep duplicity in the color abnormality generation are made.