Marcus Annius Libo was a Roman Senator active in the early second century AD. He was consul in 128 as the colleague of Lucius Nonius Calpurnius Torquatus Asprenas. Libo was the paternal uncle of the Emperor Marcus Aurelius. Beyond his consulship, almost nothing is known of his senatorial career. During the reign of his brother-in-law, Antoninus Pius, he was one of seven witnesses to a Senatus consultum issued to the city of Cyzicus in 138, which sought approval for establishing a corpus juvenum for the education of young men.