Abstract
For almost two decades, extremist groups have used cyberspace including social media networks for propaganda and radical ideologies, political, religious ideas, communication with each other and organizing actions, planning attacks in the physical world and receiving finance. Social media networks have become a “new battlefield” where extremist groups can still expand their sphere of influence more and continue spread fear and panic. Young people are at risk now so researchers must use some techniques to detect online extremism. The main objective of this paper is to provide a better understanding of the definition of extremism and radicalization, and an overview of the online extremism in textual content.