Context : In recent years it has been claimed that the length of stellar activity cycles is determined by the stellar rotation rate . It is observed that the cycle period increases with rotation period along two distinct sequences , the so-called active and inactive sequences . In this picture the Sun occupies a solitary position in between the two sequences . Whether the Sun might undergo a transitional evolutionary stage is currently under debate . Aims : Our goal is to measure cyclic variations of the stellar light curve amplitude and the rotation period using four years of Kepler data . Periodic changes of the light curve amplitude or the stellar rotation period are associated with an underlying activity cycle . Methods : Using the McQuillan et al . 2014 sample we compute the rotation period and the variability amplitude for each individual Kepler quarter and search for periodic variations of both time series . To test for periodicity in each stellar time series we consider Lomb-Scargle periodograms and use a selection based on a False Alarm Probability ( FAP ) . Results : We detect amplitude periodicities in 3203 stars between 0.5 < P _ { cyc } < 6 years covering rotation periods between 1 < P _ { rot } < 40 days . Given our sample size of 23,601 stars and our selection criteria that the FAP is less than 5 % , this number is almost three times higher than that expected from pure noise . We do not detect periodicities in the rotation period beyond those expected from noise . Our measurements reveal that the cycle period shows a weak dependence on rotation rate , slightly increasing for longer rotation period . We further show that the shape of the variability deviates from a pure sine curve , consistent with observations of the solar cycle . The cycle shape does not show a statistically significant dependence on effective temperature . Conclusions : We detect activity cycles in more than 13 % of our final sample with a false alarm probability ( calculated by randomly shuffling the measured 90-days variability measurements for each star ) of 5 % . Our measurements do not support the existence of distinct sequences in the P _ { rot } - P _ { cyc } plane , although there is some evidence for the inactive sequence for rotation periods between 5–25 days . Unfortunately , the total observing time is too short to draw sound conclusions on activity cycles with similar length as the solar cycle .