You can revise your formula to include the ISNA condition and return a blank

e.g. =IF(ISNA(your_formula),"",your_formula)

or you can use conditional formatting to change the font colour to match the background colour...

select cell and invoke Conditional Formatting...

Select formula Is from 1st drop down and enter formula: =ISNA(A1) where A1 is cell with N/A result. Click format and choose font colour. Click ok twice to exit.