How to explain CPU usage in this app?

OS: win7 64bits

I am measuring cpu usage in an application by following cpu usage results

         Cpu 1   Cpu 2    Cpu 3    Cpu 4    Cpu 5    Cpu 6      Cpu 7     Cpu 8
Max      71.8    47.6     98.4     46.8     95.4     6.2        1.9       70.3
Min      3.5     0        0        0        10.8     0          0         4.3
Average  26.652  2.10272  33.2662  2.95886  50.3894  0.0659401  0.060218  30.8496

      

        
        
        
      

    

This application is a single thread program, but when it is very busy, many processors also look busy. I don't know the reason for this, my guess is that os will put the application on a different processor to execute, even if it is one thread program (move the thread to another processor). Is it possible? Did I miss something?