Galaxy 4 Phone Persistent Freezing Screen When Using an App

Why does my Samsung GALAXY 4 phone freezes sometimes, when I am in the process of making a call or using an app? The screen freezes for 3 to 4 minutes before returning to normal operating mode. What is the likely cause of this freezing screen? How can I rectify this problem? Is it an inherent hardware or software issue? Can the network signal cause the screen to freeze and make the touch-screen unresponsive?
