I filed electronicly and owed federal tax. I paid by check. Today I got an unexpected refund without explaination. what to do?

This is a stretch but did you have any IRA or 401K distributions on 1040 line 4b?  Is line 4a smaller than 4b?  Does the amount match anything on your return?  Or did you make any estimated payments you forgot to enter?

Checks from the IRS don't arrive without explanation, although they can arrive before the explanation.  You may want to hold on to the check until you find out - you can try calling the IRS, but tax season is not a great time.

As VolvoGirl pointed out, you may have forgotten to enter a tax withholding and the IRS caught it and sent you a refund of the unused portion of your payment.  If you can determine this is the case, you're safe to deposit your check.

There is also a scam that goes around.  These days, it generally involves a fake IRS direct deposit to your bank account and then demands for you to send it back, but I have seen it done with checks.  It's always best not to deposit any surprise checks until you determine they are legitimate.

What is the problem with 1040 line 4a is less than 4b

@Whosnot

 

The IRS instructions for line 4a are a bit perplexing.

 

Many taxpayers think that line 4a should be the total of all IRA distributions and line 4b the taxable total, but that's not how the instructions actually read.

 

In some cases, the IRA distribution is added to line 4a and in some cases it is not.

 

Read the line 4a instructions at the IRS website, if you want to know more.

And it's better for 2019 since they put IRA and 401K on separate lines...4a/4b and 4c/4d.  The prior posts were for 2018 where all 1099R went to the same line 4.