The study aimed at investigating the challenges of youth radicalization as well as terrorism on the national security in Mandera County. The following objectives guided the; first to explore Kenyan government‟s reaction to threats posed by radicalization and terrorism, Secondly to assess the influence of Kenya counter terrorism on her foreign policy and to examine the drivers of radicalization in Mandera County. The study found out that, the process of radicalization entails the way by which individuals, or groups seek to reject the status quo and democratic principles and conform to their own extremists‟ ideals and principles to achieving own ideological goals. Radicalization can be violent or nonviolent and often occurs over a certain time resulting to a significant change on how individuals or people in general sense perceive themselves and the world or the environment which they find themselves. Radicalization as a concept is often misunderstood; hence many arguments have been put forward. A number of researchers have tried to come up with different conceptions and theories to explain and analyze the process of radicalization. However, the theories have not been conclusively and empirically tested. The process is however, largely perceived to begin with an initial exposure through indoctrination and training, then violent action. Many agree that individuals who are inducted into the process do not necessarily go through all the procedures needed in radicalization. Many become inducted and jihadists of violence. Mandera County presents a case of a multi ethnic and religious society with ethnic Somalis forming close to 10 percent of the population while the rest is a mixed up of different ethnic communities in Kenya making it a bedrock of radicalization. This study has also shown that the radicalizers take advantage of poverty, low level of education and perceived marginalization to influence the youth into joining radical groups, among them are the Al-Shabaab and Mombasa Republican Council. Today, Kenya hosts various radicalized groups that are ready to indulge in violence as exemplified by the restive Muslim youths in Northeastern Kenya that is giving room to radicalizing Muslims and non-Muslim Kenyan youth thereby deteriorating the national security.