EXCLUSIVE

We've learned ... the star of "Back Door Teen Mom" was on the mansion hunt this weekend in The Oaks in Calabasas -- an expensive gated community home to stars like Kourtney Kardashian, Travis Barker, Romeo, Keyshawn Johnson, Shanna Moakler and others.
One of the homes that tickled Farrah's fancy was a 4,851 square feet pad with 5 bedrooms, 6 baths ... and a $3,299,900 price tag.
It's unclear if Farrah has already put down an offer ... but with the 6-figures she made from the tape, she could definitely afford the down payment.
The monthly mortgage payments, on the other hand ... let's just say she might need to re-open the back door if she plans on staying here a while.