You can IF you challenge yourself. Before you buy, take a spin class and note the techniques used to get a good work out. Its a matter of watching your revolutions per minute, compared to the Watts you are using, and monitoring your heart rate. You Have to push it. Not every second mind you, but every two minutes you need to push yourself until you feel like you are going to die, then do a recovery, push it, then recover and so on. If you just set it to a certain resistance and mindlessly spin while watching the TV. it will burn some extra calories, but it won't be a work out.
If you want to challenge yourself without having to be so deliberate about it, get an elliptical or treadmill. Most home stationary bike users don't know a darn about how to get a good work out on the thing and I say that as someone who's been there and done that.