It appears that you have created a surface from a 2D array that has a row of 0 on the top and left edges.
Depending exactly how you are plotting, you might be able to trim that row and column before doing the plotting. Or you might be able to replace the 0's with NaN before doing the plotting. These possibilities might not work as hoped if you are using surf(), as surf() interpolates face color based upon adjacent values and NaN in particular could potentially end up "poisoning" the edges that you do want.
Another approach, depending on how you did the plotting, might be to adjust the color of those particular faces to be 'none' or NaN to make those faces transparent. You might be able to adjust the graphic object CData or AlphaData
