The Arif Agha Mosque (Arabic: مسجد عارف آغا) later known as the Imam Ahmad Ibn Hanbal Mosque is a historic mosque located in the Rusafa area of Baghdad, Iraq. The mosque was built during the Ottoman period, and it contains a small mausoleum which is purported to be the burial place of Ahmad ibn Hanbal, the founder of the Hanbali school of thought.

The mosque is an Ottoman-period structure. It consists of a prayer hall, courtyard, and a small room topped by a dome which serves as a mausoleum. The total area of the mosque is around 300 square metres, and the mausoleum room cannot hold more than 30 visitors. Parts of the mosque are in disrepair and currently undergoing an extensive restoration.

In 1937, the remains of Ahmad ibn Hanbal were supposedly transferred to the Arif Agha Mosque after the cemetery he was buried in was flooded by the Tigris. Later historians have doubted the story, saying that it is inaccurate and erroneous. Before this, a domed mausoleum had been built over the grave of Ahmad ibn Hanbal, but it was destroyed repeatedly.

• List of mosques in Iraq