Another 58 people were injured in the blast in Muqdadiya, Diyala province, some 80km (50 miles) from Baghdad.
Several leading figures in the Shia-dominated Popular Mobilisation Forces were among the victims.
The so-called Islamic State (IS) said it organised the bombing - a day its militants killed at least 70 in a Shia area of Baghdad.
Diyala security officials said two Shia commanders attending the funeral were targeted and killed in Monday's attack, Reuters reports.
The officials said the bomber approached the commanders and blew up his explosive-laden vest.
IS said earlier that its militants had organised Sunday's blasts in the Shia district of Sadr City and more attacks would follow.
The mainly Sunni group, which controls large swathes of northern and western Iraq, has attacked numerous Shia targets in the country recently.
At least 38 people have been killed by a suicide bomb at a Shia funeral north-east of Iraq's capital, officials say.