John Mystikos (Greek: Ἰωάννης ὁ Μυστικός; fl. ca. 924–946) was a Byzantine official, who served as the chief minister (paradynasteuon) of the empire in the early reign of Romanos I Lekapenos. After being suspected of designs on the throne, he was deposed and sent to exile in a monastery. He eventually recovered a place at court, leading a three-year mission abroad in the 930s, and apparently regained his former high position with the rise of Constantine VII Porphyrogennetos to sole rule in 945. He is last mentioned as leading an embassy to Muhammad ibn Tughj al-Ikhshid in 946.