You can combine "sitting" or "standing" with another action in this way. A few more examples:

I was sitting on the couch doing my homework.

Amy and I were sitting there talking and this guy I know walked by.

They're still standing outside the train station waiting for someone.

Describing an action in this way with "sitting" or "standing" usually makes it sound like the action wasn't very important or interesting. However, it can also sound relaxing, like in the example above. Another example is:

I'm just sitting in a cafe, having a cup of coffee. What are you doing?