The version of GNU Octave available in the official repositories of Linux Mint (and Ubuntu) is out-dated. I think the Mint 13 repositories have Octave 3.2.4, whereas 3.6.3 is the latest, released in September. Fortunately for those who want to avoid the time-consuming installation from source, there is a PPA where latest releases of Octave are maintained for Ubuntu versions up to 10.04 LTS. For Linux Mint 12 Lisa (based on Ubuntu 11.10) and Mint 13 Maya (based on Ubuntu 12.04 LTS), the same PPA can be used.
Details of the installation:
GNU Octave PPA (mtmiller/octave)
Open a terminal and execute the commands:
sudo add-apt-repository ppa:mtmiller/octave
sudo apt-get update
sudo apt-get install octave gnuplot
The new installation will remove older conflicting versions (if any) in the system.
At the time of writing, the latest Octave available with this PPA is 3.6.3, same as the one available at the official GNU Octave sources page.