When you purchase the hardware you get the specification sheet which shows the temperature of the processor under specific condition. For example, most of the processors from INTEL are in the following temperature slots : 45°C - 65°C.
In case of intel G2020 2.9 ghz temperature, the specification online from INTEL shows the following : 33°C - 65°C. You may find the working condition processor under the range within the said number.
Idle temperature should be 33-40 normally. If the temperature is high then make sure you are giving proper cooling around. You can add additional fan and the cooling pad inside your desktop hardware. Also cleanup your computer and see if any app or virus is making the processor heat up. There are many ways to fix this but one has to look at your processor to understand the cause.