Thanks for following up, @Deborahkwok.
To clarify, this is the issue you are experiencing with the Roku mobile, the keyboard pops up after opening the Roku device using the Roku mobile app. In this case, when the issue occurs what screen page shows on your Roku device? Are you able to exit the keyboard that pops up or it is stuck on the screen? Does the keyboard consistently open even when trying to access other features on the Roku mobile app?
Keep us posted with the details.