If you are a W-2 employee, your employer should not be withholding NJ taxes at all. NJ and PA have tax reciprocity. If all your NJ income is W-2 wages, it is taxable only in your home state of PA.
If your employer did incorrectly withhold NJ taxes in 2016, you would have to file a non-resident NJ return (showing zero NJ income), if you wanted those taxes refunded.
If this is your situation, you should file Form NJ-165 with your employer, to certify your non-residence in NJ. Here's a link to that form: http://www.state.nj.us/treasury/taxation/pdf/current/nj165.pdf
The tax reciprocity applies to W-2 wages only. If you have other types of NJ income, such as rental income from a property located in NJ, you'd have to file a non-resident NJ return.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
