One of its affiliates claims to be. According to AFP:

An Al-Qaeda linked Sunni group in Iraq said it used chemical weapons to attack targets in Baghdad, in a statement on an Islamist website.
Jaish al-Taefa al-Mansura (Army of the Victorious Community) said its fighters fired shells filled with chemical agents at the interior ministry, foreign ministry, the “green zone” and Baghdad’s security academy.

The interior ministry in Iraq appears to be confirming that there have been mortar attacks but not that chemical weapons have been used. Meanwhile, AFP adds that Jaish also “warned Sunday that it would use chemical weapons against ‘occupation’ and Iraqi forces unless they halted their offensive against rebels in the northern town of Tal Afar.”