Both Jews and Arabs are Semites - they belong to the Semitic race (not the Ashkenazi Jews though)...
So, technically an anti-Semite is someone who hates both Jews and Arabs, and Arabs can't be anti-Semitic, just as Jews can't be anti-Semitic.
But the Zionists have appropriated the word 'Semite' to mean specifically Jews, so they can stain anyone who criticises them as 'anti-semitc', even if the criticism has nothing to do with race, ethnicity or religon.