The present work is stimulated by a recent detection of moderate line profile variations of selected lines on a time scale of minutes in the FORS2 spectra of the A0 supergiant HD 92207 (Hubrig et al. 2014). Recently, we investigated the variability of line profiles of selected OBA stars with the multi-mode focal reducer SCORPIO on the SAO RAS 6-meter telescope (BTA). We discovered regular variations of the H and He lines in the spectra of the O-type star HD 93521 (O9.5 III) with periods of ˜4-5 and ˜32-36 minutes. A possible origin of short time-scale spectral variations is discussed.