Have you installed the drivers?
However these are the instructions for Mac OSX
Install the Software
Copy the Arduino application into the Applications folder (or elsewhere on your computer). If you're using an Arduino Uno or Mega 2560, you don't have any drivers to install. Skip ahead to the next step.
If you're using an older board (Duemilanove, Diecimila, or any board with an FTDI driver chip.
You will need to install the drivers for the FTDI chip on the board. You need to download the latest version of the drivers from the FTDI website. One downloaded, double click the package, and follow the instructions in the installer. You'll need to restart your computer after installing the drivers.
Check if it works for 10.9.