Yes, it is safe to put things above a radiator provided that you leave a small gap of 5cm or more between the top of the appliance and the item or the shelving.
With that said, you should look to avoid placing things directly on top of a radiator for any significant period of time when the central heating is turned on. By doing this, you could damage the items, and risk burning yourself when picking them up.
To find out more, explore our dedicated blog, How to decorate above a radiator.