The Collaborative International Dictionary of English v.0.48:

Unbelieving \Un`be*liev"ing\, a.
   1. Not believing; incredulous; doubting; distrusting;
      skeptical.
      [1913 Webster]
      [1913 Webster]

   2. Believing that the thing alleged is not true;
      disbelieving; especially, believing that the Bible is not
      a divine revelation, or that Christ was not a divine or a
      supernatural person. "Unbelieving Jews." --Acts xiv. 2.
      [1913 Webster] -- Un`be*liev"ing*ly, adv. --
      Un`be*liev"ing*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unbelievingly
    adv 1: in an incredulous manner; "the woman looked up at her
           incredulously" [syn: incredulously, unbelievingly,
           disbelievingly] [ant: believingly, credulously]