That 'looks like' Giant Hogweed. By 'tall' would you go to 5 or 6 feet - if so then definitely. This a an invasive non-native species and can cause you problems. Do not let your bare skin come into contact with it as it can cause serious burns which will haunt you for several years when you go out in the sun. It should be removed carefully and taken to the local landfill site where you should notify the operator of what you have brought in.
Personnally, I would suggest you get a responsible professional gardener to deal with it - before it sets seed.

Oh dear that sounds bad!
Glad I asked and thanks for the advice.

at only 5-6 ft it could just be the normal wild common hogweed [Heracleum sphondylium] just grown well due to the fertile soil. I sometimes get it that tall and taller. Giant hog weed is 10ft or more.
are the stems blotched purple? that tends to bea characteristic of the giant hogweed. either way it needs to come out. it will have a tap root like a parsnip. wear gloves just in case it is the giant one.

Thanks...It flowered at 5ft so hopefully it's the common type. Either way I removed it ...carefully....this morning.
There was no purple botching on the leaves

Having just researched this I now think my plant was Angelica.

unless you definitely planted it I don't think the flower head is right for angelica. I seem to remember the heads are more rounded. still think common hogweed.