Police arrested a 40-year-old woman at a home in Seven Hills on Thursday following a report that the Toongabbie MP was assaulted at Seven Hills at 8.30am on Wednesday by a woman with whom he admitted to having an affair last year.

A spokeswoman said the woman was taken to Blacktown police station where she was later charged with assault occasioning actual bodily harm.

Earlier, police said they had been told that Mr Rees, 46, was "walking through a shopping centre when he was approached by a woman who struck him a number of times".

The former premier did not need medical treatment but Blacktown police were notified, a spokeswoman said.

Mr Rees, who served as NSW premier between September 2008 and November 2009, announced in March he would not seek re-election in 2015.

His decision followed his resignation as opposition police spokesman in 2013 after details of an extra-marital affair were reported by the media.

Last month, he announced he would become the chief executive of non-profit group Public Education Foundation.

The woman will appear in Blacktown Local Court on October 8.