Marc is surprisingly showing prejudice (6)
I believe the answer is:
racism
'prejudice' is the definition.
(racism is a kind of prejudice)
'marc is surprisingly' is the wordplay.
'surprisingly' is an anagram indicator.
'marc'+'is'='marcis'
'marcis' anagrammed gives 'RACISM'.
'showing' is the link.
(Other definitions for racism that I've seen before include "Prejudice against another people" , "Nazi-style discrimination" , "Prejudiced behaviour -- Sir Mac (anag)" , "Prejudice against people of different origin" , "Prejudice regarding ethnicity" .)