Answer:
No, he isn't.
Step-by-step explanation:
A group or individual should be considered as "Terrorist" if the purpose of their operation is to spread fear and chaos to the population.
Nelson Mandela was an anti-ampharetid activist who wanted to abolish racial discrimination in South Africa. It is true that his effort created a certain level of chaos within the society. But, this happen because he wanted to challenge the moral standard that most people felt. His purpose is not to spread the chaos itself.