Thawed ground beef should be good for up to two days if kept refrigerated at 40 degrees Fahrenheit or below. Ground beef should not be left at room temperature for more than two hours or more than one hour at 90 degrees or above.
The safest way to thaw ground beef is in the refrigerator, where cold temperatures slow the growth of bacteria. If the ground beef is defrosted in the microwave, then the meat should be cooked immediately after thawing since microwaving may partially cook some of the meat. Ground beef also should be cooked immediately if thawed using cold water.