Yes, it is. When battery i being charged, it's getting warm due to the chemical reaction taking place inside of it. When device is running CPU-intensive applications, it warms up too due to the CPU heat dissipation (circuits are getting heated by the current flow).

So, unless it's getting really hot (might happen in case of very hot weather plus direct sun rays over the extended period of time plus some high CPU load - device will save itself by doing a thermal shutdown), it's fine.