Getting Response time

Hi,
I am running an experimrnt where a subject sees a stimulus and has to answer after hearing a beep. I use getsecs to record response time. The subject answers "yes" or "no" by pressing either the left or right arrow key.
 
After I ran the experiment, I found that some of the reaction times were as low as 0.02 milli seconds. I really dont think it can be that low. I think I may be doin something wrong here... Can anybody share matlab code with me that is used to record the response time. If you would like to help me correct the mistake by modifying the code, I can send you my code.
 
Regards
Hari