ProgressBar running faster after each onclick in android

I am Stuck here with this application in android. In my application i am trying to implement a progressbar which shows timer for certain seconds. When the Button is clicked the timer should refresh and again start from 0 in progressBar. For this I am using Thread.

The Problem is, When I Click the button the Thread calls the timer function and each time the thread is getting faster and faster. I couldn't resolve it and not having any idea what is going in background. This is my code for Timerfunction

public void setTimer()
    {
        prog=0;
        progress.setProgress(prog);
        if(flag){
        t= new Thread(new Runnable(){
            public void run()
            {
              while(prog<100)
              {
                prog+=1;
                handle.post(new Runnable(){
                    public void run()
                    {
                        progress.setProgress(prog);
                        if(prog==progress.getMax()&& flag){
                         call_fun();
                        }
                    }
                });
                try
                {
                  Thread.sleep(time);
                }
                catch(InterruptedException e)
                {
                    Log.i("Error", null);
                }
              }
            }
        });
        t.start(); 
        }
    }

I called this function in another function called RandomGeneration. If the button is clicked the randomgeneration is called and the set timer is activated everytime. But the progressbar is running faster after every click. It is constantly running in the same specific time. For example if it runs for 3 seconds in the first click, its running 2 seconds in the second click and getting faster considerably.

Can anyone please try to find what is happening in this code. Thanks in advance..!!