Yes, the American ancestors of modern native Americans ultimately came from Siberia and Alaska, somewhere between tens of thousands and hundreds of years ago, depending on the group. However, those Siberians ultimately came from Central Asia in turn, and Africa before that. Therefore in the strictest sense, humans as a species are native only to Africa. That's not what is meant by the term "Native" in "Native American" though. Instead the entire category of "native" is an invention of the colonial period, one that was eventually turned into an actualized identity. Native in this sense is simply a recognition of aboriginal claim to parts of the continent and identity rather than a statement about evolutionary origin.