I contributed max allowed $5000 to Non-Deductible IRA with after-tax money in Jan 2012 and then immediately converted all $5000 to Roth IRA. Non-Ded IRA had no funds prior to this. This is sort of backdoor way to contribute to Roth IRA if you are not eligible to contribute directly to a Roth IRA.

Then in Mar 2012, I rolled over my old 401K (previous employer - pretax money) to a Rollover IRA. Will this activity have any tax implications given that I did a Roth conversion earlier in Jan 2012. If yes, can I undo this 401K rollover or can I transfer rollover IRA to my current 401K plan with current employer?

In order, yes and maybe.

When you do the calculation of the taxable/nontaxable portions of the conversion you look at 12/31/2012 traditional IRA balance. See Form 8606, part I.

Your current employer can, but is not required to, accept a rollover into your current 401(k). Before you do so, make sure you really want to do it.

Phil
Rule Your Retirement Home Fool