For some soon-to-be retirees, retirement will look a lot like their 9-to-5 life.

Nearly 3 out of 4 Americans plan to work beyond traditional retirement age on at least a part-time basis, according to a recent Gallup poll.

A separate AARP study found that 37 percent of working Americans ages 50 to 64 said they intend to work after retiring from their current careers. Of those, 44 percent plan to enter new fields.

Of course, working in "retirement" has many financial benefits. Aside from the income, it can allow you to preserve your retirement savings for later in life and even keep building those assets in tax-advantaged retirement plans. (Contributions to traditional IRAs can only continue up to the year in which you turn 70½, but if you earn income past that point, you may be able to continue making contributions to a Roth IRA indefinitely.)

But that extra income can also come at a cost if you're not careful, according to Marcy Keckler, a vice president of financial advice strategy at Ameriprise Financial.

For ambitious retirees, here's are three things to watch out for: