Preventing Reset during ESD
Assuming the reset pin is pulled up, putting a 100nF cap to ground at the pin generally won't hurt you. The bigger issue here is ESD protection. Where is the ESD getting into the circuit? Cable shields, connectors, the enclosure, any user interface buttons or knobs, , etc. all need to be considered. The energy from the event needs to be safely dissipated, with the how depending on the source. I strongly recommend read through John Barnes' articles on ESD protection.