Definition from Wiktionary, the free dictionary
- Past participle of mistake
- I'm frequently mistaken for my brother.
- This is a clear case of mistaken identity.
- (with a copula verb, often with about) Having an incorrect belief.
- I think you must be mistaken.
- He admitted he was mistaken about the budget numbers.
Usage notes 
- The phrase if I'm not mistaken (and variations) is used to indicate that one is uncertain about something one has said.
- Nouns to which mistaken is often applied: identity, belief, notion, view, assumption, impression, idea, thinking, identification, diagnosis, interpretation, person, opinion, conclusion, judgment, conception, perception, theory, reading, concept.