Can I run wires from two separate circuits through the same box?
The answer is yes you can have 2 separate circuits in the same box (they can have a splice also but not needed in your case). The only concern would be the total box fill. Based on the NEC the wire fill would be calculated at 2.0 for each conductor for 14 gauge wire and 2.25 for 12 gauge wire. The device or switch counts as 2X for the largest wire connected to it or each in the box. All the ground wires count as 1X of the largest ground in the box. If the box has clamps they are counted as 1X of the largest wire. With the numbers added up they need to be smaller than the listing on the box for cubic inches. If more information is provided on the size of the wires entering and exiting the box and total number of devices we can help with the calculation.