The most common cause of foot numbness is improperly fitting shoes. Check the size guide for sizing and if you're between sizes go for the next size up. This is because your feet will swell slightly so a tight shoe will contrict blood vessels, making toes and feet go numb.
Another cause could be improperly aligned cleats. You could consider positioning cleats further back towards your heel to offer more even pressure across your foot.
A pair of cycling shoes can make all the difference to your comfort and performance in the saddle. They’re lighter and stiffer than causal shoes with a better fit. If you plan on riding regularly then a pair of shoes should be high on your wish list – you'll never look back.