I want to plot mean annual precipitation data for a region. I downloaded the precipitation dataset for 1900-2014 from University of Delaware site in netCDF format. Whenever I try to open the dataset in ArcGIS, it gives me more 1000 (114 years * 12 months = 1368 rasters) of rasters with each raster containing the precipitation data of a particular month. I wanted to know that how can I get an average raster data out of the 1368 rasters.
You need to use a tool such as The netCDF Operators, or NCO. Have a look to the user guide http://nco.sourceforge.net/nco.html.
I have no idea how your data is organized, but have a look to this discussion, it seems to be your case: https://sourceforge.net/p/nco/discussion/9830/thread/9809999b/