Yea of course:
my_data = new LoadVars();
my_data.onLoad = function(success){
if(success){
my_textfield.text = this.myVar;//assign the content of the textfile to the textfield
trace(my_textfield.maxscroll);//at this point you can make sure the file has been loaded
}
}
my_data.load("my_file.txt");