The man was allegedly yelling expletives and expressing his opposition to the Covid-19 vaccination mandates and police.
He was compliant as officers arrested him. He was later charged with wilful damage, and was due to appear in the Oamaru District Court on March 9.
Dean, who was in Wellington at Parliament yesterday, said she was "really heartened and comforted" that members of the Oamaru community had alerted her and police to the vandalism, and a "very kind person" had cleaned it off.
None of her staff were in the office at the time, and she was "very pleased" that was the case.
"That's what I don't like, is that my staff are in the firing line, and that's not where they should be."
Dean said there were always opportunities for people to raise their concerns with her directly and peacefully.
Oamaru's Severn St wall was also targeted by vandals yesterday. Racist graffiti appeared on the Oamaru stone wall overnight and was reported to the Waitaki District Council about 7am.
Waitaki Mayor Gary Kircher said the graffiti contained "vile" racist and expletive messages, which had "absolutely no place in our community".
"Tagging of any kind isn't welcome, unless it's actually part of an art thing, but to have that vile racism is definitely totally out of order and not part of being a caring community that we want Oamaru and Waitaki to be.
"If the culprit, or culprits, are found, I hope they get the book thrown at them."
He thanked Dooleys Masonry and the traffic management team for their prompt response in cleaning the tagging off the wall.
The police had not received any reports of the Severn St graffiti, and it was not believed to be connected to the Thames St vandalism.
