The couple, who have been on holiday in the country over the festive period, were said to be planning to fly family and friends out for a small ceremony, reported OK magazine.
"Originally they wanted to fly everyone to Cabo San Lucas, Mexico, for a small barefoot-on-the-beach ceremony, but that plan was scrapped after the details were leaked," a source said.
Aniston and Theroux are apparently eager to get married.
"They are both incredibly excited. Jen can't believe it's actually happening. Jen's in a super place at the moment. She's on an all-time high," the source added.
Aniston and Theroux recently denied fresh claims that the actress is expecting a baby.