Ground beef cooks quite fast. It doesn't need more than 5 minutes (depending on the base of your pan and the amount of meat of course). Just take a piece and rip/cut it open. If it's brown inside, and not red or pink, it's fully cooked.

How long does it take to cook ground beef?

On most stove tops, browning a pound of ground beef takes approximately 7 to 10 minutes.

How can you tell if ground beef is undercooked?

Cook ground beef to an internal temperature of 160 °F as measured with a food thermometer. The color of cooked ground beef can be quite variable. At 160 °F, a safely cooked patty may look brown, pink, or some variation of brown or pink.