It's not. There are two types of electromagnetic radiation: ionizing and non-ionizing.

Ionizing is the radiation that is bad for you because it also shoots little tiny particles at you that damage your DNA. Think X-rays

No-ionizing radiation doesn't shoot tiny particles at you, so it's mostly safe. Microwaves use this type, and it's the exact same radiation your wifi router uses (which is why it can cause interference)

The worst a microwave oven can do to you is give you a burn since they work by heating up water molecules. But, that would require you to trip the door switch and putting a body part inside.

So, in conclusion, it's basically impossible for a microwave to harm you with EMR unless you're actively trying to make it harm you.

Also, as an added bonus but of knowledge, it's completely safe to microwave metal, if it's in the right shape. Some microwaves even have a metal rack for heating up casseroles and such (mine did at one point)