A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
I'm assuming you mean that the "pop-up" actually appears when you paste, not when you copy, correct? If so it is the Paste Options button as AaAa_08 mentioned, but you do not need to disable the feature. Just press the esc key when it appears.
If something is popping up when you copy please provide a screen shot, the present Version of your Office software [as indicated in Excel> About Microsoft Excel] as well as additional descriptive details about the exact steps to reproduce.