I'm assuming this is a separate Roku device connected to a TV, not a Roku TV that has Roku functionality built in.
If Settings > System > Control other devices > 1-Touch play is checked, an inadvertent touch of the remote can do this. If yours is checked, try unchecking and see if that takes care of it.
The downside: You'll have to use the TV's remote to switch to the input to which your Roku is connected.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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