For the normal ConTeXt file,
texexec --pdf myfile.tex
XeTeX is able to handle UTF-8 or UTF-16 documents natively, without any interference or configuration from ConTeXt. If you do want ConTeXt to process UTF-8 characters specially, then you can activate it with <cmd>enableregime</cmd><tt>[utf]</tt>. Be aware that you are then limited by the named glyphs that exist in the unicode vector files (<tt>unic-0xx</tt>). However, it is generally desirable to enter UTF documents without any regime notated, and let XeTeX work its magic.