The US military said the bus drove over the mine on Thursday in the town 180km west of Baghdad. Another two people were injured. Half of the bus was mangled and destroyed in the blast, according to witnesses.
US occupation forces stationed in Tikrit were deployed to the area.
In other violence in the area, occupation soldiers killed seven alleged resistance fighters in three separate clashes on Wednesday, revealed military sources on Thursday.
More Iraqis killed
Most of the other clashes on Wednesday occurred near Baquba, 75km southeast of Tikrit.
In Abu Kharma town, 15km from Baquba, four alleged Iraqi fighters were killed by US gunfire by troops during a raid, said a military spokesperson. One US soldier was wounded.
The troops captured 31 alleged loyalists of detained ousted leader Saddam Hussein during the raids. Several weapons were confiscated, including 19 AK-47s, six rocket propelled grenades, seven kilogrammes of plastic explosives and three homemade bombs, said occupation authorities.
In Khalas, 10km northwest of Baquba, a US Army patrol fired at two Iraqis digging a hole in the ground, killing them both. The US army claimed the men were planning to plant a bomb but there were no other independent reports.
And in Jalula, near Tikrit, US soldiers opened fire at two people who allegedly attacked them with automatic weapons, killing one of them and injuring the other, said military sources. They were apparently planting a homemade bomb.