The world has witnessed the emergence of radical and extremist ideology which poses a threat to international security by influencing society towards excessive acts. Radical and extremist ideology is not only limited to certain territories but covers the entire Islamic world including South-east Asia. The evolution of ideologies from the West based on a doctrine of violence leads to conflict or clash of cultures and civilization, especially for societies in South-east Asia. Hence, the purpose of this article is to identify the forms of radical and extremist threat which apply specifically in South-east Asia. In addition, this writing aims to identify methods or measures in handling the issue of radicalism and extremism which occurs in South-east Asian states. Writing methodology is qualitative with a historical and current phenomena approach based on data findings through literature review and document analysis. Research findings conclude that radical and extremist ideology poses a threat to society and state so as to challenge multiculturism policy of a state. The push and pull factor also plays a role in spreading this ideology within society Therefore, this article attempts to bring a reply narrative based on pro-active methods and measures in the prevention of and dealing with this complex global issue.