Frisian is not a dialect, and is not usually spoken outside of Frisia (the Dutch province). In German Ostfriesland they do speak a German dialect with Frisian roots.

i was simplifying. the difference between dialect and language is fluid. plattdeutsch (low german) is also considered a language, as is luxembourgish. frisian btw is also spoken in nordfriesland (in schleswig-holstein) and there are a few speakers of saterfriesish which is the last remaining dialect of east frisian.