Can I buy property from SC category person

You have not specified whether the land is an agricultural land or residential but assuming it was agricultural land if the patta (government documents issued on the person who owns the land) issued under SC condition he can't sell the land. There is a condition in the patta upto certain period normally 25 years from the date of issue, the land should not be either sell, lease or any other purpose except by his own use. Otherwise a SC candidate sell is normal without any restriction.