Screen locks when receiving calls

[sc0ut]

When I receive and answer a call the screen locks. If I need to use keypad input, speakerphone etc,, I cannot. This happened on my last Sony phone - Satio, and was never fixed. I recycled it. I hope this is not to be a repeat of the same issue!! Samsungs Active mini could be the answer?!

[Uliwooly]

Settings > apps  > all > phone > clear data > restart your phone 

[Alexander1]

Does the screen lock and doesn't respond to touches or does the screen gets black when answering/calling someone? 

[sc0ut]

Thank you for the replies. I think I have it sorted now. The proximity sensor had been obscured by an ill-fitting case.

[Kosi]

I think the problem starts when the current call is longer than what is set under Settings-Display-Sleep. So if the call is longer than the set period (in my case 30 sec) the screen does not come back automatically when you remove it from your ear to use the numeric key, or to check anything during the call or even to end the call. I always have to "wake up" the screen by pressing the power button.