The phrase "no problem" is a stock phrase (or, some would say, viral "meme") which seems to carry a wide variety of contradictory meanings. Some people associate it with the British Empire and certain former colonies, e.g. Jamaica, Nigeria.
It is typically used to mean "I've taken care of it" or "No thanks are necessary; my effort was no problem for me." It has no real meaning outside of the context in which it is used.
A phrase or idiom dictionary translation of "no problem" might read "I'll take care of it" or "there's nothing to worry about". However, it effectively means nothing other than "I'm not going to give you any other assurances" - and thus ends a conversation about whatever risk is about to be incurred. Some think it means roughly the same thing as "shut up".
Although the phenomenon of such slowly-reversing meanings is widely observed and agreed to exist, there is little study of the issue or why it may occur. Some think it has to do with the process of colonization, and misleading the colonial ruler; others think that it is just an example of etiquette, i.e. a "white lie" that the utterer actually believe causes "no problem". For the utterer, at least.
