Possible Pre-Civil war Massachusetts State Militia button. 1820s to 1840s. 1 piece raised design gilded brass. Many of this particular variety made at this particular time period were still manufactured in Britain and are labeled as such (for example, rich quality/london on the backside as opposed to yours which is Standard treble gilt with possibly the word "rich" still currently obscured). This may indicate an American made variant of this type. If you have an Albert's book handy or even not check the interwebs for Alberts MS27 and you'll find a similar example of yours (lined background, pebbeled shield with indian, north star (to the left of the bow if you are looking at it straight on) albeit with different backstampings but like I said, probably just a variant of the MS27.
