The word "am dubious" suggests uncertainty or skepticism about something. Some antonyms for this phrase could be "am certain," "am confident," or "am convinced." These words indicate a strong belief or assurance in something. Other possible antonyms include "am convinced," "am resolute," or "am steadfast." These words indicate a firm and unwavering belief or resolve in a particular matter. Additionally, one might use antonyms such as "am enthusiastic," "am optimistic," or "am hopeful" to indicate a positive attitude or outlook towards a situation, indicating that one is not feeling doubtful or uncertain.