Source : Webster's Revised Unabridged Dictionary (1913)

Involuntarily \In*vol"un*ta*ri*ly\, adv. [From {Involuntary}.]
   In an involuntary manner; not voluntarily; not intentionally
   or willingly.

Source : WordNet®

involuntarily
     adv : against your will; "he was involuntarily held against his
           will" [ant: {voluntarily}]