Washington (AFP) - A St Louis County police officer is being investigated after apparently bragging on Facebook about how he spent his "bonus" for working during recent protests in Ferguson, Missouri, the Guardian reported.

The officer, Todd J Bakula, apparently generated extra income while policing protests marking the first anniversary of the police shooting of black teen Michael Brown.

That shooting set off weeks of unrest last year and became one of a series of high-profile deaths calling into question how US police officers interact with black men.

The anniversary protests, initially peaceful, devolved into violence and looting on Sunday night.

In a Facebook posting under the user name TJ Thekoola, Bakula wrote he was "spending my annual Michael Brown bonus on a nice relaxing bicycle ride trip" and staying at a bed and breakfast with his wife, the Guardian said.

St Louis County police spokesman Shawn McGuire told the Guardian that the post was "controversial" and would be investigated by the department.

Bakula did not respond to questions from the newspaper.