No, it's fine, actually. I don't believe the tracker actually actively checks every torrent's IP addresses to ensure there's only ever one at a time.
You can definitely take a torrent you downloaded on one computer and redownload the data on another computer while it's still seeding on the first computer. Just remove it once it's done.
If you leave them both seeding on two machines, though, or if you redownload it more than a couple times, in the long run someone is bound to notice.