She has been removed for allegedly bringing the party into disrepute.
Ms Patterson recently criticised the party's decision to overlook her for the South Belfast assembly seat vacated by Jimmy Spratt, and instead appointing former special adviser Emma Pengelly.
Mr Robinson said Ms Patterson has a right to appeal her expulsion.
He said party officers "unanimously decided to expel her earlier this week".
He added that he believed "there has been some correspondence" between the party and Ms Patterson since she was informed of the decision.
Ms Pengelly took her place in the Northern Ireland Assembly in September through the co-option system, which allows parties to replace departing MLAs with a party colleague without a by-election.
It has been used extensively by many of the parties in the assembly.
Within a month of her selection as an MLA for South Belfast, Ms Pengelly was appointed as a junior minister in the Office of the First Minister and deputy First Minister.
She had previously worked in the department as a special adviser to the first minister for almost nine years.
Last month, Ms Patterson, a former deputy lord mayor of Belfast, said she had been annoyed by Ms Pengelly's dual promotion.
"There is a principle, in my book, of giving someone who has earned something the chance, rather than someone who does not have one solitary vote, who has never stood for election, who has never run the gauntlet of an election," she said.
"It it not sour grapes. Anyone in my position would feel exactly the same - not surprised, but let down.
"I thought I was worth a little more."
Ms Patterson also said last month that her party's return to the Northern Ireland Executive after the publication of a report on paramilitaries had shocked her "to the core".
She said she had major difficulties with the move, and had been considering her position in the party.
Belfast councillor Ruth Patterson has been expelled from the Democratic Unionist Party (DUP), its leader Peter Robinson has told the BBC.