Hi Hossain,
I just tried your scenario in my system.
1. I created an opportunity.
2. Navigated to Products tab.
3. Added a Product --> The Product Category was automatically added.
I had to remove Product also as it was not possible to remove only the PC and saved.
The system threw error message to enter product and PC.
As the system itself does not let you save if the PC is not entered, the notification will not generate.
regards
Preethi