The students were travelling to their homes in Tunis, a religiously mixed district of the Iraqi capital, when gunmen in a car sprayed their bus with bullets.
No other details were immediately available.
Police also said earlier today that at least four college students were killed and 25 wounded in a mortar attack on the Ibn al-Haitham college in nearby Adhamiya district.
Adhamiya drew international attention last month when the US military began building a wall to protect the Sunni Arab enclave from surrounding Shi'ite districts.
Adhamiya residents complained bitterly about the controversial 5-km, saying it would isolate them from other communities and sharpen sectarian tensions.
The construction of the wall came as the US military deployed thousands of extra soldiers around Baghdad as part of a security crackdown aimed at dragging Iraq back from the brink of all-out civil war.
REUTERS SS ND1932