Graffiti on the door and windows of Mrs Dean's office in Thames St reads: "Freedom" and ''F*** all politicians and police''.
A police spokeswoman said police received a report of a person spray-painting the building at about 10.30am today.
She confirmed a 57-year-old man had been arrested charged with wilful damage, and would appear in the Oamaru District Court on March 9.
Mrs Dean, who is in Wellington at Parliament today, said she was ''really heartened and comforted'' that members of the Oamaru community alerted her and police to the vandalism, and a ''very kind person'' was cleaning it off.
"Maybe that just reflects the community response to what's been happening,'' she said.
None of her staff were in the office at the time, and she was ''very pleased'' they were not.
''They're incredible loyal and hard-working people,'' she said.
"That's what I don't like, is that my staff are in the firing line, and that's not where they should be.''
Mrs Dean said there were always opportunities for people to raise their concerns with her directly, peacefully, and ''in a law abiding manner''.
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