Yes, and many people do just that. People who are past full retirement age may work and earn any amount without losing any of their Social Security benefits.
But before you reach full retirement age, Social Security will subtract money from your benefit check if you exceed a certain amount of earned income for the year ($14,160 in 2010). The limit applies only to earnings from work; it does not apply to income from such things as savings, investments, pensions, or rental property. In other words, earnings from these sources will not affect your Social Security benefits.
The Social Security Administration has added a special twist for the year in which you reach full retirement age. During the 12 months prior to your birthday, you will lose one dollar of benefits for every three dollars you earn over a set monthly limit ($3,140 per month in 2010). After your birthday, you can earn any amount of money without losing benefits.
To learn more about how and when to claim retirement benefits, see Social Security, Medicare & Government Pensions: Get the Most Out of Your Retirement & Medical Benefits, by Joseph Matthews with Dorothy Matthews Berman (Nolo).