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The study of a possible connection between magnetic activity and orbital period variation in close binaries is a very interesting work. Recently, the orbital periods of four chromospherically active binaries, ER Vul, UV Psc, AR Lac and BH Vir, are analyzed. It is discovered that the orbital periods of UV Psc and BH Vir oscillate with periods of 61 and 9.12 years, and the orbital periods of ER Vul and AR Lac show periodic variations with periods of 31 and 47 years respectively while they undergo secular decrease. The mechanisms that could explain the changes in the orbital periods of the four systems have been studied. The period variation of UV Psc may be caused by the cyclical magnetic activity in the primary component, and the magnetic activity in secondary component of AR Lac can explain its periodic component in the orbital period changes. For the other two systems, BH Vir and ER Vul, the cyclical magnetic activity in one or both of the components can explain the cyclical orbital period changes of BH Vir and the periodic component in the changes of the orbital period of ER Vul. These results suggest that the periods of the orbital period oscillations in the four systems may be the magnetic activity cycles.