As mass irregular structures are more influencing on the behavior of the structures, it is investigated the effect of these irregularities according to the probabilistic approach. Comparison of seismic performance of ten regular and irregular 6-story concrete special moment frame is done, based on the Mean Annual Frequency (MAF) method. The probability of collapse in all irregular models has exceeded the 1 % that is permissible value specified in the ASCE/SEI 7-16. The largest rate of increase in the probability of exceedance the collapse limit state in 50 years, is about 34.1 % in mass irregular structures. Also the results of this study have indicated that both the level of irregularity and the location of irregularity in height is effective in the probability of exceedance the collapse. It should be noted that the critical story in the mass irregular structures is the top story (fifth story).