Religious extremism is a phenomenon that is very rampant on the table of discourse both in local and international forum. The research looked at religious extremism among Muslims and Christians in Nigeria, using "Boko Haram" sect as a case study. It presented the causes and effects of religious extremism. It is discovered in the study that the Nigerian society, religious extremism (violence and crisis) is more rampant in the Northern part of the country than any other part. The study recommended among other things, that religious educational enlightenment in Nigeria should be properly taught which would be centered on religious tolerance and understanding. The study recommended that the Nigerian constitution should avoid constitutional segregation as it pertains to religious matters, hence the need for constitutional review. The study also recommended that proper involvement of medical personnel and psychologists should be put in place, through which psycho centers and rehabilitation centers should be established to re-orientate the minds of the religious extremists instead of killing them.