In the default setup, Tera Term emulates VT100 keyboard. Therefore some numeric keys do not work like them in other applications. For example, the "Num Lock" key does not work as "Num Lock". To disable the emulation and use numeric keys in normal way, edit the keyboard setup file KEYBOARD.CNF to disable every items in the [VT numeric keypad] section by using the word "off", like the following (see also Keyboard setup file):
[VT numeric keypad] Num0=off Num1=off Num2=off Num3=off Num4=off Num5=off Num6=off Num7=off Num8=off Num9=off NumMinus=off NumComma=off NumPeriod=off NumEnter=off PF1=off PF2=off PF3=off PF4=off