Yes. You need a margin account and your net account value must be $2,000 or higher.
1) Go to the "Watchlist" tab on the main screen.
2) Look up a stock and tap on it.
3) Check for a blue downward arrow icon on the top right of the stock page.
4) If the icon is there, you can short sell this stock.
5) Tap the "Trade" button on the bottom left.
6) Select "Sell."
7) Fill in the required fields.
8) Submit the order and wait for it to be filled.
9) If the order is filled, go to the "Home" tab.
10) The short position will be displayed in your "Position" section as a negative quantity.