The Collaborative International Dictionary of English v.0.48:

Negativeness \Neg"a*tive*ness\, Negativity \Neg`a*tiv"i*ty\, n.
   The quality or state of being negative.
   [1913 Webster]

WordNet (r) 3.0 (2006):

negativeness
    n 1: the character of the negative electric pole [syn:
         negativity, negativeness] [ant: positiveness,
         positivity]
    2: characterized by habitual skepticism and a disagreeable
       tendency to deny or oppose or resist suggestions or commands
       [syn: negativity, negativeness, negativism] [ant:
       positiveness, positivism, positivity]
    3: an amount less than zero [syn: negativity, negativeness]
       [ant: positiveness, positivity]