No, at the moment there is no option to update your status. After 4 minutes of inactivity you will be marked as away.
The different statuses are as follows:
Note: the desktop app will keep you online if you're active on your computer (any click, keypress, tap) but the Web version can only detect activity in the browser tab.
- Green circle: Online.
- Orange circle (containing hands of a clock): Away.
- No circle: Not online.