Hi Aniket,
normally this system behavior is know when you are on a test system because on limited performance.
What is happening? Each system access will cause an entry in SM12 - by this the system takes care that not two users will be able to change data in the same time. (to avoid conflicts)
So somehow this entry will stay even the user exit the transaction. Why? Long story :-)
At the end normally this is not happen - or the system admin (basis team) will take care that the situation will not be there anymore.
If this will not help you can tell your users to proper log out from the screen - but all this thoughts are useless from my side. At the end the system has to take care about clearing the lock entry in SM12!!
Best regards,
Sigi