Thanks for the note. Doe staking the batteries out of your remote resolve the issue?
If not, it's possible that someone in your house (connected to the same wireless network as the TV) is controlling the Roku TV using the Roku mobile app. You can disable this setting in Settings>System>Advanced system settings>Control by mobile apps>Network access - and choose 'Disabled'.
If the issue stops from there, that would likely explain the behavior you are seeing.