TV reporter Ayham Khazaal and his brother Nashwan Khazaal were put to death at the weekend, the Aranews website said, citing local human rights activist Khalid Musill.
"After being held for several months, IS militants executed Ayam and Nashwan on Saturday," Musill was quoted as saying.
Ayham Khazaal, who worked for the 'Sama al-Mosul' local TV channel, and his brother were accused of spying for the international coalition against IS and for the Iraqi security forces, Musill said.
The Khazaal brothers were executed in front a large crowd after an IS militant read out their death sentence.
All coalition 'spies' including journalists and aid workers would meet the same fate, witnesses cited the militant as warning.
Dozens of journalists accused of spying have been executed by IS in Iraq including at least 25 in July last year in Nineveh province surrounding Mosul.
Mosul is the largest Iraqi city still under IS control. US-trained Iraqi forces last week retook the Hit region backed by war planes from a US-led coalition.
Iraqi forces retook the western city of Ramadi in December.