Error "Incorrect Multibyte Characters" When Attempting to Load CSV

When I create simple data in CSV format (UTF-8) in Excel (the first line is alphanumeric) and try to read it in R with read.csv("filename", header=T)

make.names(col.names, unique=TRUE): 
   '<ef>sa<bf>area' contains invalid multi-byte characters 
> 

The error appears.
I checked and found that there was an encoding problem, but the conditions should have been met because it was in UTF-8 format, but it didn't work.

I would appreciate it if you could tell me how to solve it.