hdmi cec and related sections are enabled within android, but when i turn off mi box, my pc warns like 'no signal shutting down in 3 minutes' . i check all the settings in the tv, but could not find anywhere to disable (i disable any power saving things i found)
are they any option within mibox/android ecosystem to prevent this?
You should disable hdmi cec on your box.
This isn't related to HDMI CEC. Your TV has a function that turns the TV off automatically if there is no input signal present on that HDMI port. If there is a setting to disable this, it would be in your TV's settings. I do wonder why you would want to leave your TV on in that condition...?
Disable HDMI CEC
The way that your TV and MiBox are "talking" is through CEC.
To stop this you should be able to set your TV to CEC ARC only or even disable it.
Optionally, you could disable CEC in the MiBox.
Doing one or the other should bring an end to that annoyance.
There is one other possibility and that is your TV is "looking" at or "watching" the HDMI port and is shutting down when it "sees" the signal on that port turn off. Though I think the chances of it being this are pretty slim.
I hope that you found this info to be helpful/useful.
Best of luck in getting this annoying "feature" disabled...