The blast happened at the party headquarters for the Patriotic Union of Kurdistan.
Iraqi President Jalal Talabani is a member of the PUK.
Police said the explosion destroyed part of the building in eastern Mosul's al Tamim neighborhood, with most of the casualties coming from the party's membership. Mosul is located about 250 miles (400 km) north of Baghdad.
Also Tuesday, the U.S. military said a deadly weekend blast in Baghdad that killed 63 Iraqis and wounded 140 others was caused by a series of insurgent attacks.
Initially the U.S. military said the blasts were the result of a gas explosion, despite the Iraqi government's insistence that car bombs and rockets were to blame.
Two car bombs touched off the gas explosion in Baghdad's Zafraniya neighborhood, leveling a residential building, according to the military statement.
The blasts were part of a coordinated attack involving four car bombs that detonated in a 30-minute time span, destroying four buildings within a 1-mile radius.
It is the second time in two days that the U.S. military and the Iraqi government had publicly disagreed over the events surrounding suspected insurgent activity.
The U.S. military released a statement Sunday saying U.S. and Iraqi forces surrounded the Iraqi Ministry of Health complex, and arrested five people identified by an Iraqi tipster as being involved in kidnapping six Iraqis from a nearby hospital.
The ministry denounced the arrests, and demanded the release of the five men, who it said are personal bodyguards for Health Minister Ali al-Shammri.
Al-Shammri is closely aligned with radical Shiite cleric Muqtada al-Sadr, who also leads an influential bloc in Iraq's parliament. Al-Sadr's Mehdi Army militia is blamed for operating death squads targeting Sunnis in the Iraqi capital.
The ministries of transportation and electricity also have strong ties to al-Sadr.