Yes. And if box 2a is blank then it might be taxable.
The IRS gets a copy of the 1099-R and expects to see it on your tax return or they can tax all of the box 1 amount and send you a bill.
many trustees leave 2a blank because they don't know how much, if any, is taxable. for example if it was from a traditional IRA and you made non-deductible IRA contributions to any traditional account you would have basis which would reduce the taxable amount of the distribution. the trustee doesn't know that. also in cases of 401k's rolled over to IRA's
A 1099-R for a Traditional IRA cannot have a blank box 2a. Traditional IRA'a 1099-R'a are required to have the same amount in box 2a that is in box 1 and also have the box 2b (taxable amount not determined) checked and the IRA/SEP/SIMPLE box checked. That combination allows the taxable amount to be modified if there is a non-deductible basis on an attached 8606 form.
<a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/i1099r_18.pdf">https://www.irs.gov/pub/irs-pdf/i1099r_18.pdf</a> Page 12
401(k)'s rolled into an IRA, if a direct rollover, will always have box 2a a 0 (zero) unless it is a Designated Roth direct rollover, then box 2a must be calculated by the administrator, but is usually the same as box 1.