Yes, salary arrears are taxed. However relief u/s 89(1) can be claimed.As per Section 89(1), tax relief is provided by recalculating tax for the year in which arrears are received and the year to which the arrears pertain; and the taxes are adjusted in the
year in which they were due. In simple words, you do not pay more taxes if there was a delay in payment to you and you were in a lower tax bracket for the year you received the money.
Note: Form 10E has to be filed before filing of the Income Tax