When you register for Twitter there is an option for you to “protect” your account.
What that means is that people will have to send a request to follow you and you will have to approve them. This is great if you are planning on devulging secret information or detailed personal stories or locations that you don’t want anyone to have access to.
If you are using Twitter for business purposes I would not suggest locking your account, but rather creating a personal one if you feel you need to seperate the two.
Check out this great post on the topic of protecting your tweets.