Really trained athletes can work out with heart rates like that. Us mere mortals need to be careful.
The purpose of exercise is to fool the body into thinking that it needs to be fitter than required for our daily activities. That is, if we have been desk jockeys or couch potatoes for a long time, our bodies get used to being fit enough for that activity level. If we want to be fitter, we have to work harder than we're used to. But since we are only fit enough to be desk jockeys or couch potatoes right at the moment, then we are capable of doing only a little bit more than our daily activities.
You said that you checked your heart rate while you were exercising. This is good. Do you have your own heart rate monitor or were you using one at a gym? It might be worth it to invest in one if you haven't already. Then, when you exercise, pay attention to the heart monitor, not to any arbitrary speed preset on the treadmill or exercise bike. The important thing is to exercise a little
harder than your body is used to -- not to whatever someone else thinks you "ought" to be able to do. You're exercising your
heart, not some generic one from from some standard list of averages.
It is also a good idea to get a physical checkup by your doctor to rule out health problems that would be causing your heart to over-react. There might be some underlying problem that you don't know about. This is why it is recommended that us couch potato folks get an exam before starting up an exercise program.
Congratulations on getting moving!
And it's good that you are asking questions about your heart in the early stages of your program.