There's no reason to necessarily be concerned, if your only indication on the status of your tax return is that it is still being processed. Please don't worry about just that. The bars on the IRS.gov's "Where's My Refund"
webpage change all of the
time, as do the messages. Not all tax returns are identical, and so they move through the
IRS processing system at various speeds. Other factors causing delays and increased refund
processing times for many people this year are several new laws and executive orders
that the IRS has been charged with implementing, including those of the PATH act.
If your tax return is chosen for further review, then the website should state that clearly, and also let you know to expect an IRS notice by mail. (You haven't observed that happen, have you?)
who do have their returns held for review, and who expect to receive an
IRS notice, tell us that such a message appears clearly on the Where's My Refund
website. The behavior that you observe is most
likely an indicator that your tax return is simply moving normally through the
processing system (slowly this can seem sometimes). It could also be that the IRS is checking for
additional information on something related to your tax return . . . perhaps causing a small delay.
If enough time passes after filing (21 days after e-file, or 6 weeks after paper file), and there is no new information, at that time the IRS indicates that you can call them, using the phone number provided on their Where's My Refund website.
For now, the best recommended course of action is patience. The IRS doesn't always move as fast as taxpayers would like (especially when waiting for a refund). Also, as noted above, the 2016 tax year may be particularly slow, due to factors that are outside of our control.
If you are asking instead about your state tax return (if applicable), the same general advice and cautions also apply, but with one additional observation. Speaking from experience and practice, most state tax refunds typically take longer to be issued than IRS tax refunds. In other words, the average taxpayer anticipating a tax return can expect to get their federal refund before their state refund.