Aniston, who was married to actor Brad Pitt for five years before they got divorced in 2005, got engaged to Theroux last August.
"Jen is going to great lengths to keep the wedding details a secret so it does not become a huge media circus like her wedding to Brad," thesun.co.uk quoted a source as saying.
"Just a few dozen of their closest family and friends will be there. But news is beginning to leak that the date is just a few weeks away now," the source added.
The couple doesn't want to marry under media glare, and hence, they might opt for a quieter place like Hawaii.
"Jen doesn't want to get married with photographers buzzing around her head in helicopters. Justin just adores Hawaii. It's his favourite place in the world and he has a little house on the island of Kauai," a source said.
"But they both love the island and the idea of a laid back Hawaii wedding in the sunshine. The have looked at some expensive villas including one where they enjoyed a romantic holiday in 2011," the source added.
Actor Ben Stiller, who is good friend of the couple, might be of some help.
"And Ben Stiller, a big buddy of Justin's, has a house over there too so that could be a surprise option," a source said.