You have a few options for dealing with this.

1) This is probably the easiest and has already been mentioned. You can open the "computing preferences" window in your BOINC client and tick the box labeled "Suspend GPU computing when computer is in use".

2) If you wanted your GPU to be utilized at all times, you could try changing which GPU your computer uses as its primary GPU. If you have a dedicated card, your computer will probably default to using that wherever possible. You can however override this in your Nvidia control panel. This will make your computer use the integrated graphics for "mundane" tasks like UI and display driving. Your integrated graphics should be perfectly capable of doing this for most low intensity tasks like handling the display, web browsing, document editing, etc, but you will probably want to use an application specific override to tell it to use the dedicated card instead if you need to do anything like games, 3D modeling, rendering, etc.

3) If you have issues with only certain programs, you can tell BOINC to pause GPU computing only when those specific programs are running. This is a good option if you dont have any problems with usability with most simply tasks like web browsing, document editing, general computer use, etc, but you DO have issues when running specific programs like a game or a modeling program, etc.

3.1) You can also use any of these three settings in combination with each other. For example, you can set it up so that GPU computing is enabled whenever the computer is not in use (no keyboard presses, mouse movement, etc) for at least 5 minutes AND a specific program (Lets say blender or Autodesk Inventor, which you might run and walk away from you computer so they finish rendering a particularly complicated scene or something) isn't running.