Does not look like a Mauser to me. Look at the trigger and the trigger guard, they look very rudimentary. The Germans would not design some thing like like. I would make two guesses, it is Japanese or Russian. Both countries were producing rudimentary firearms during WWII toward the end.
All Mausers that I have seen, not matter what country they are from (except German) will have other marking on the top of the receiver. Most of the time you will find them with a crest of some sort. The German models will have a swastika stamped on them somewhere. You will often fine the Waffen SS lightning bolt on those also. In addition they will also have 98 stamped on the receiver somewhere.
Some of the German WWII will have letters stamped on the receiver denoting where they were produced. ie. concentration camps
http://burnfan0.tripod.com/sitebuildercontent/sitebuilderpictures/.pond/k98_6.jpg.w560h328.jpg
Look on the reciver and bolt for a chrysanthemum. it will look like this:
http://www.radix.net/~bbrown/pictures/japanese/mum.gif
If you see that then it is Jap WWII.
Of course, if it is a WWI Mauser, what I said above will not apply. Here is a pic of a WWI mauser.http://freepages.military.rootsweb.com/~worldwarone/WWI/Weapons/images/rifles-page95-sm.jpg