EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
Confusion; Situational Awareness
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
Our PDC stated that we were cleared via the ZZZZZZ 2 departure out of ZZZZ.  This is a southwest bound heading off of runway XXL.  It was my FO's leg and she briefed us on the departure and the heading.  We were cleared for takeoff and once airborne I pushed the heading button which was set to the required heading.  My FO then began a right hand turn and asked me to hit the nav button.  I was asked to do this during my after takeoff flow and didnt even think twice about her request to nav her up.  The airplane then began intercepting a track to ZZZZZ on pink needles which is before ZZZZZ1.  ATC then told us to go direct ZZZZZ1 at 3000 FT.  We were at 1800 FT when ATC gave us these instructions.  I remember thinking that something didnt seem right.  ATC then asked us why we were already starting the turn before 3000 FT.  At this point we were trying to correct back to the 237 heading.  Atc then came back and instructed us to go direct ZZZZZ1 at that time.  He then questioned us on what we were doing.  I said that we were going to ZZZZZ and he said that the PDC was to fly the departure which stated a southwest bound heading. He then siad he had to file a report and that no other aircraft were in the vicinty at the time.  We then switched frequencies and continued to ZZZ1.  Some threats is that we were a new crew operating our second flight toghether.  I felt confident in her ablity as a pilot and when she asked for the nav button to be pushed I did what she asked for.  I thought maybr she herad a clearence that i didnt and i just did what she asked for without questioning it.  I should of inquired about it and verified before pushing the nav button.  The big error that occured; was that we were on the wrong heading and not following our clearence.  We deviated from what we were suppose to be doing.  Once we were informed of the error we began correcting.
EMB-145LR Captain reported deviating from cleared track on departure when the flying First Officer called for LNAV prematurely.