When you live in a big city, it's statistically likely that you'll catch a glimpse of someone else's life through their window at one point or another. Even if you're not actively trying to be voyeuristic, it's hard not to glance when you see a group of people laughing, or a scene from your favorite TV show through a stranger's window. For this reason, a lot of people use curtains to conceal the inner-workings of their home, particularly if they're changing or engaging in sexy time.
However, that isn't the case for everyone, some people feel completely fine with the potential of strangers seeing them, others may not be thinking of it, and some even like it. If you're in the confines of your own home, you can and should be able to do whatever you want with your body.
That being said, if you have huge windows near the street, people are going to see you. So, if you're walking around the house naked, they'll also likely see that.