The Collaborative International Dictionary of English v.0.48:
Unpleasant \Un*pleas"ant\, a. Not pleasant; not amiable or agreeable; displeasing; offensive. -- Un*pleas"ant*ly, adv. -- Un*pleas"ant*ness, n. [1913 Webster]WordNet (r) 3.0 (2006):
unpleasantly adv 1: in an unpleasant manner; "he had been unpleasantly surprised" [ant: agreeably, enjoyably, pleasantly]