Should I make extra mortgage payments?

I am at a new job that doesn't offer a 401k. Now I have that money and don't want to waste it. I already bought an IRA but still have extra. I don't have credit card debt and have an emergency fund. My car loan is only 1.9% and my mortgage is 4%. My interest payments aren't enough to itemize so I don't get any tax benefit. I don't believe I'll ever go into foreclosure. The stock market is to risky for me so it seems like a solid 4% gain for me to make the extra mortgage payments. Am I missing something?

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