Fraught with uncertainty or doubt "dubious about agreeing to go" - doubtful
Open to doubt or suspicion "he has a dubious record indeed"; "what one found uncertain the other found dubious or downright false" - doubtful, dubitable, in question, doubtable
Not convinced "they admitted the force of my argument but remained dubious"
See also: dubiously, dubiousness, incertain, questionable, uncertain, unconvinced, unsure