Marcus Annius Flavius Libo was an ancient Roman Senator who lived in the second half of the 2nd century and first half of the 3rd century.
He was a member of the Nerva–Antonine dynasty. Libo was a Patrician and came from Hispania Baetica. His grandfather was Marcus Annius Libo who was made suffect consul in 161. His father of the same name was a legatus of Syria and was poisoned possibly by his cousin the Roman emperor Marcus Aurelius. Libo became ordinary consul in 204. He was related to Marcus Aurelius through their mutual ancestor Marcus Annius Verus who was consul three times; and by marriage to Roman emperor Antoninus Pius who married his grandfather's sister.
- Prosopographia Imperii Romani, A 648