A true believer in the Almighty is always an activist. A proactive activist that is! Especially the followers of the final Messenger (SAW), as He was sent as a propagator of all of good & benefit, and taught us to work carefully & diligently in the removal of everything harmful.
As a muslim, you cannot seperate the concept from activism based on revelation and the teachings of the final Messenger (SAW) from yourself.
If you lack the necessary knowledge of true activism; it is upon you to seek it.
It takes good people to do nothing for evil to spread, and we begin to lose a piece of ourselves everytime we witness oppression towards God Almighty or His creation, and choose to do nothing about it.