KA-BAR in Massachusetts, is it legal?

So I bought a KA BAR yesterday at an army surplus store in salem. I love it and its my first real combat knife. My question is it legal to carry on you in a sheath? Its got a 7 inch fixed blade. I know switchblades and automatic knives are illegal. I just want to know if I can carry it in my car or on my belt somewhere. Please dont patronizing me with saying its not "right" to carry a knife around. I just want to know If I can carry it with me and the police wont arrest me for having it or confisacting it especially since i payed $70 for it.