Is it normal to "extract a paper" from a master thesis?
It is plagiarism only if you do not properly cite it.  

If you have not published the thesis itself, of course you can publish parts of it or summaries of it or even the whole thing unchanged.  The requirement to avoid "self plagiarism" is to cite.  For example, in the introduction write:


  This paper is taken from my thesis [title] done in [date] at [school] under the direction of [advisor].