Yes it is normal. It just means that linux system uses more of the free ram in filecache, ie making your load times faster (it automaticly uses less ram for files if free amount drops to certain levels).

Linux holds the most recently used files in the ram cache so subsequential loads of the same files are really fast, if you use dropcache it drops the recently used files out of the ram, and thus if apps loads some files, it needs to access the flash vs ram to load the file, ie it makes loading slower (also affects application startup times). So in short people using dropcache are just newbies

For further reading you should read this: http://www.linuxatemyram.com/