"I have NEVER knowingly taken any banned substance and when I found out the news last night I was totally shocked," Miller said on Instagram.
"My team and I stand for integrity, decency & honesty and together we will stand to fight this with everything we have!"
Miller also said the test was a voluntary one that he was happy to take and added that the results came one week after another voluntary test he took was completely clean.
The boxer's camp have requested a B sample be tested, the BBC reported, and if that sample comes back negative Miller can apply for a licence again.
ESPN reported that Miller had tested positive for the banned substance GW1516, which boosts endurance and helps athletes burn fat, citing three sources familiar with the matter.
"Remember don't believe everything you hear and see. The facts will prevail and I shall be vindicated," said Miller.
"I don't have anything to hide and the truth will make itself known."
(Reporting by Frank Pingue in Toronto; Editing by Peter Rutherford)
