I am using ggplot2 library and am working with the qplot command I know I can save my output as an anti-aliased image file by using the following command after my qplot
If you have Cairo installed (see the other answers), to save it as an anti-aliased PNG, just change your code to:
ggsave(file="filename.png", type="cairo-png")
as specified here.
But for what purpose do you want to "see a plot on the monitor as anti-aliased graph" or "anti-alias my plot windows"? If you mean like in the Plots window (tab) in RStudio, I am not sure that can be done, it serves basically just as a preview. I suggest you save the graph to a file and then use this file to display it or for any other purpose.