NO, Native Americans are NOT of Mongol/Siberian descent.
All evidence indicates that both North and South America were inhabited 50,000+ years ago. Some archaeologists maintain that humans inhabited the Americas over 100,000 years ago, The evidence found has been geofactual and not cultural.
Neither Asians nor Europeans existed at the time Native Americans were living in the Americas. The mongoloid characteristics did not even exist in Asia until 7,000 years ago. So any mongoloid characteristics people THINK they see in Native Americans did not come from Asia. No matter where people say Native Americans came from, all evidence proves it false.
This video states that the mongoloid characteristics did not exist in Asia until after Native Americans were known to be living in the Americas
First Americans
http://www.youtube.com/watch?v=Ff2g-G0ogVI&feature=channel
This data shows a “World Population Relationship Tree“. You will see that Native Americans are placed on a totally separate branch from all other populations. (pg 2)
The Arctic Connection: Alaska to Siberia
http://www.dnatribes.com/dnatribes-digest-2008-10-25.pdf
Virtually without exception the new evidence supports the SINGLE ancestral population theory. Native Americans are more closely related to each other than to any other existing Asian population.
A unique variant (an allele) of a genetic marker in the DNA of modern-day Native Americans, dubbed the "9-repeat allele," the variant occurred in all of the 41 populations that they sampled from Alaska to the southern tip of Chile. Furthermore, the allele was ABSENT in other ASIAN populations
2009: Native Americans descended from a single ancestral group
http://www.physorg.com/news160214945.html
Pedra Furada in the North-East of the Brésil probably represents the oldest archaeologic human site known in America. A total of seven charcoal samples coming from various hearths were subjected to analysis. The samples proved to be old beyond the limit of 48,000 years, indicating ages of 55,000 with 60,000 years.
2003: Padre Furada (Brazil)
http://www.speedylook.com/Pedra_Furada.html
http://www.abc.net.au/science/news/stories/s990775.htm
2004: New Evidence Puts Man In North America 50,000 Years Ago
http://www.sciencedaily.com/releases/2004/11/041118104010.htm
2008: Humans walked America 40,000 years ago
http://www.itwire.com/index2.php?option=com_content&do_pdf=1&id=19484
Native Americans are their own race.
Native Americans are the largest homogenous race on earth.