I have to build backlinks for the website and thats not related any forum categories. Is there any problem if i add those unrelated links in forum websites? Does Google consider it as low quality backlinks.?
According to current Google rules all the irrelevant back-links are treated as spamming and it is bad for your website. To index your website as Google friendly, you should to work on relevant forums and blogs. Which have OBL not more than 50 for quick ranking.
OBL stands for outbound backlink. In other words, a link to your site from other website. Generally I don't think it will hurt much. It is very general that people will put some links on their sites which seemed are "irrelevant", e.g. a personal blog. He make like coca-cola and then link with their websites, also he may be a fan of Kobe Bryant, so he links to Nike basketball website, etc.. So are these links are really spam?? Hard to tell.