It can be passive income. If you put in the work initially to make a website that gets free search engine traffic every day it could make you pretty passive income for a long time.
It can take time though to create a website with good quality content, and then it takes some time to rank in the search engines.
Also, note that it requires a bit of work every now and then to keep your content up to date which can be required to keep your free traffic coming in.
It is also required to do some work related to the renewal of your domains, web hosting account, and maybe some tech support related to optimizing and keeping your websites online.
There could also be work related to the bookkeeping of earnings and expenses and such.
The two most important skills for making passive income with affiliate marketing, I would say, is writing skills and SEO skills. You could learn those skills as you go though. The most important thing is just to get started and also having a bit of dedication to keep trying for a while.
See all questions and answers in my affiliate marketing FAQ