Can anyone please tell me how easy it is to take a taxi from the Boston North Station? Do you have to walk very far? Is it safe outside the station?

North Station is a subway stop and the origin (or end) of many Commuter Rail trains as well as a couple of Amtrak (e.g., Portland). A busy place with plenty of cabs, and in a neighborhood that's full of businesses, restaurants, and other travelers. What's your destination?

Thanks for such a fast reply. And your reply is good news. I'm going to Boston Common. Thanks!

take the subway from north station(green line) to park which sits on the common. Easy, fast, inexpensive.

Sorry I'm late getting back to this thread -- I agree with cigalechanta (of course !) -- unless you have a lot of luggage, take the Green Line to the Park Street subway station, which is right at the corner of the Common. A taxi would not only cost more, but will probably encounter traffic, which will further increase your cost and transit time. Green Line uses cars that are more like trolleys rather than regular subsays -- you have to climb up steps when boarding the car.

The Common is a rather large, 5-sided space. If you're going to, say, the corner of Charles and Boylston, that's at the Common but quite fairly long walk from Park St. Given that the OP appears to be unfamiliar with Boston, a taxi might be a more suitable solution. And, if taking a taxi, the OP would do well to give a much more specific location than "Boston Common" (for example, a specific address).