An Iraqi security force spokesman for the Joint Coordination Centre, which handles information and is a liaison between US and Iraqi forces, said that the Tuesday air raid destroyed one house, killing the people inside.
Another four houses were hit and three people were wounded in the raid on Monday night, he said.
"We have this information from the Iraqi police and army in Baiji," said the spokesman, who declined to give his name.
The US military had no immediate comment.
Baiji has seen considerable fighting from forces opposed to the US-led military presence, including efforts by fighters to disrupt oil and fuel flows through its refinery, the biggest in Iraq.
The closure of the refinery last month is causing shortages of fuel across the country.
US forces have used air power increasingly throughout the past year; official military data show that only one strike was carried out in March, and the average in the first quarter was five strikes a month compared with more than 50 in the last quarter.
Iraqi medical staff, police and political leaders - particularly in the Sunni Arab-dominated west and north of the country - have reported civilian casualties in such raids.
US commanders say they make every effort to minimise that risk.