The IRS says I over paid and sent me a check back. I am reluctant to cash the check thinking they will want the money back. I used turbo tax to do my taxes. Please advise

There are a number of factors here that need to be considered when this occurs:

1. The IRS will send you a letter that discusses the overpayment; what was changed, sometimes a line by line comparison of what you filed versus what the IRS is using.  You need to review this letter to see if you agree with any adjustments.
2. The letter and refund check don't always come together, so if you get the check first you should receive the letter shortly thereafter.
3. What the IRS letter should discuss is why the change:
1. Was there a transposition error when you entered the information?
2. Did you underestimate any estimated tax payments made?
3. Did you accidentally forget to include withholding on a W-2?

I would not cash the check until you receive the letter and can review it to see if you agree with the changes.  If you do agree with the adjustment(s) then deposit the check.  If you don't, then you can follow-up at that point.