Modern materials clothing and furniture contains man made fibres that can produce a lot of static.
Any two materials rubbing together will produce static. and the only way to get rid is to ground (earth) it.
PCs are earthed through the three pin plug to the PSU and therefore there should not be a problem.
Problems occur from PCs on the floor if they are stood on carpet or tucked somewhere that never gets clean (like under desks) as they can fill with dust that then causes overheating.