As others pointed out, you need to give more information – from the information you present it's not clear what type your data really is. It is possible that you have a data.frame, in which case you can go with Simon's answer. However, your output could easily be a vector with named elements, too:
dat <- c(PC1=6.403056e-04, PC2=5.433502e-04, PC3=7.888467e-05, PC4=6.776798e-05, PC5=2.589316e-05)
> dat
PC1 PC2 PC3 PC4 PC5
6.403056e-04 5.433502e-04 7.888467e-05 6.776798e-05 2.589316e-05
> class(dat)
[1] "numeric"
In which case you already have what you are after, except for element labels. If you really needed to get rid of those you could drop them like this:
> names(dat)
[1] "PC1" "PC2" "PC3" "PC4" "PC5"
> names(dat) <- NULL
> dat
[1] 6.403056e-04 5.433502e-04 7.888467e-05 6.776798e-05 2.589316e-05
However, removing them probably has no real benefit.