Java ArrayList Concurrent Modification

What potential runtime error is present in the removeIfCondition method of the code segment shown?

import java.util.*;

public class IteratorIssue {
    private List<Integer> list = new ArrayList<>();
    
    public void removeIfCondition() {
        if(!list.isEmpty()) {
            for(Integer num : list) {
                if(num < 5) {
                    list.remove(num);
                }
            }
        }
    }
    
    public void addValue(int value) {
        list.add(value);
    }
    
    public static void main(String[] args) {
        IteratorIssue ii = new IteratorIssue();
        ii.addValue(3);
        ii.addValue(7);
        new Thread(() -> ii.removeIfCondition()).start();
    }
}