is my cpu overclocked?

Solution
I see no problem here?
Perhaps you aren't sure the actual speed of your CPU...

See this: https://ark.intel.com/products/97147/Intel-Core-i5-7400-Processor-6M-Cache-up-to-3_50-GHz
Base clock: 3Ghz
Boost: up to 3.5Ghz

So, there's no problem at all...
The Intel Turbo Boost is automatic, it's activated when the CPU needs an extra power, overclocking itself to handle the current process it's calculating atm, and after it finishes, it will go back to it's base clock.

May you detail your doubt better?
I see no problem here?
Perhaps you aren't sure the actual speed of your CPU...

See this: https://ark.intel.com/products/97147/Intel-Core-i5-7400-Processor-6M-Cache-up-to-3_50-GHz
Base clock: 3Ghz
Boost: up to 3.5Ghz

So, there's no problem at all...
The Intel Turbo Boost is automatic, it's activated when the CPU needs an extra power, overclocking itself to handle the current process it's calculating atm, and after it finishes, it will go back to it's base clock.

May you detail your doubt better?
 
Solution

Did you not read @manddy123's post? The i5 7400 has a base clock of 3 GHz, but will automatically turbo up to 3.5 GHz under load. This is clearly listed in the specs for that CPU, and is standard behavior for all i5/i7 CPUs.