With restrictions, yes. You can only do it once per product (and only five per user) and you have to apply to Customer Support as the serials are different.
moving this to the Photoshop forum
You can only transfer from PC to Mac if the version is current. So you can't transfer CS5 to a Mac, but you can upgrade your CS5 PC to CS6 Mac.
If you subscribe to cloud version you can use either OS.
"If you have a previous version, you cannot swap to a different platform or language of the previous version. Instead, it's necessary to upgrade."
What Curt Y said.
Since CS5 and been superseded by CS6 (and now version CC in the Cloud), your options are
- to crossgrade to CS6 (which is still available to purchase), or
- join the Cloud and get Photoshop CC.