I noticed this right around the time I read this article. Apparently, there is some preliminary research that suggests mental strain, while not burning any excess calories, might make us more hungry.
I can see why. We need energy for work. Food is energy, and mental tasks are definitely still work. But it just doesn't seem fair!
I am at a job all day where I sit and stare at a computer screen. It actually makes me miss the days when I was a waitress!
The best advice I can think of: take short walks during the day in which you give your mind a rest and your body some physical exertion. Exercise is also a good way to get energy without taking in any calories.