Currently, there is no adult content available in the Roku Channel Store. However, some private channels may contain adult content (see What is a “Private Channel”?). Private channels can only be added to your Roku player with a code from the channel developer using your account login information. Rest assured, you are always in control over what kind of content appears on your player.
Roku Ready TVs: designed for Roku streaming
How do I add a private or beta channel to my Roku player?
To add a private or beta channel you must first get a code from the channel developer. Second, you must have a Roku account, and you must be logged in. This ensures that unauthorized users cannot add a private channel to your Roku player without your consent. Third, you enter the code provided by the channel developer here. After linking, the private or beta channel will appear on your Roku player’s home screen, alongside your other channels (like Netflix, Amazon Instant Video, etc).