The Collaborative International Dictionary of English v.0.48:

Mischievous \Mis"chie*vous\ (m[i^]s"ch[-e]*v[u^]s), a.
   Causing mischief; harmful; hurtful; -- now often applied
   where the evil is done carelessly or in sport; as, a
   mischievous child. "Most mischievous foul sin." --Shak.
   [1913 Webster]

         This false, wily, doubling disposition is intolerably
         mischievous to society.                  --South.
   [1913 Webster]

   Syn: Harmful; hurtful; detrimental; noxious; pernicious;
        destructive.
        [1913 Webster] -- Mis"chie*vous*ly, adv. --
        Mis"chie*vous*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

mischievous
    adj 1: naughtily or annoyingly playful; "teasing and worrying
           with impish laughter"; "a wicked prank" [syn: arch,
           impish, implike, mischievous, pixilated,
           prankish, puckish, wicked]
    2: deliberately causing harm or damage; "mischievous rumors and
       falsehoods"