Grampian Police has been told to take action after a large rise in complaints against officers and reports of racially-motivated crimes.
Complaints against officers increased by almost 70% from just under 300 in 2006/07 to almost 500 in 2009/10, according to a new report.
The number of reported racially-motivated crimes rose from 449 to 879.
However, detection rates improved from 59.9% in 2006/07 to 69.3%, above the the Scottish average.
The Accounts Commission and Her Majesty's Inspectorate of Constabulary for Scotland compiled the report.
It said Grampian Police and the joint police board performed well, but that more progress could be made.
The report said that the force considers members of the public are more prepared to make complaints because they have confidence in its willingness to deal with them.
It said that evidence suggests that the force was meticulous in recording complaints and this, coupled with changes in recording processes, may have accounted for some of the increase.
The report revealed an overall reduction in recorded crimes since 2006/07 and crimes of violence, indecency, dishonesty and reckless behaviour were at their lowest level for seven years.
Her Majesty's Inspector of Constabulary, Andrew Laing, said: "Grampian Police force is performing well and demonstrates many of the elements of best value.
"Levels of public satisfaction are high and improving and, overall, crime rates in the area are falling.
"However, it is unclear why recorded instances of racially-motivated crime and complaints against the police have increased and the force should make further efforts to understand and explain this."
The force and the board are to produce an improvement plan to show how they intend to address the findings.
Chief Constable Colin McKerracher said: "This is an excellent report that acknowledges the tremendous effort that has gone into our strategy for delivering the highest quality of policing for the people of the north east of Scotland.
"Over the past few years we have seen our officer numbers rise, crime rates across the region fall to a seven-year low and with detection rates for violent crime at their highest level over the same period."
The force said it recognised and acknowledged the areas for improvement.