Weka can read csv files, however, if csv file's format is not fully satisfy Arff file standard, it may cause some problem. For example, I found loading a time series CSV file to Weka cause errors repeatedly.
There have been some posts on using python to convert csv to arff online, but I think the code is a little lengthy and not always work.
Is there a safer and quick way to convert csv to arff in R?
For Mac User (as RWeka for mac has not fixed yet):
For CSV file which cannot be loaded to Weka using CSVLoader, use R's foreign library to convert dataset from csv file to arff file
The following R code can convert a timeSeries dataset from csv into an arff file accepted by Weka
Simple, use the package RWeka