The monthly index known as the Chicago Fed National Activity Index rose from minus 0.23 in June to minus 0.15 in July. The three-month rolling average for the index -- less volatile than the month-to-month reading -- also rose, climbing from minus 0.24 in May to minus 0.15 in June.
The index has now read below zero for five consecutive months, the Fed said.
The index is a broad measurement of U.S. business activity, using a weighted average of 85 indicators based in four main categories: Production and income; employment, unemployment and hours worked; personal consumption and housing, and sales orders and inventories.
The index uses zero to represent average growth. As such, July's index shows growth slightly below the historic trend.
The Chicago Fed said 38 of 85 indicators made positive contributions in July while 47 made negative contributions. From month to month, however, 53 of the indicators improved from June to July while 32 "deteriorated," the Chicago Fed said.