It happened shortly before 11 o'clock this morning at Northside Elementary School.
According to the school's principal, a teacher received the envelope around 10:45 and took it to the main office where they called 911 and evacuated the campus.
Siloam Springs Police responded to the school and the principal says they determined the powder to be baking soda.
Students and faculty were readmitted in to the building a short time later.
According to Benton County Sheriff's Office investigator Kenneth Paul, this is the 15th suspicious letter received around Siloam Springs recently, some containing powder while other made vague threats.
Just yesterday, officials were called out to Dayspring Cards for the second time in less than a month after a envelope containing white powder was mailed to the Siloam Springs-based business.