  We analyze the rest-optical emission-line ratios of star-forming galaxies at
2.7<=z<6.5 drawn from the Cosmic Evolution Early Release Science (CEERS)
Survey, and their relationships with stellar mass (M_*). Our analysis includes
both line ratios based on the [NII]6583 feature -- [NII]6583/Ha,
([OIII]5007/Hb)/([NII]6583/Ha) (O3N2), and [NII]6583/[OII]3727 -- and those
those featuring alpha elements -- [OIII]5007/Hb, [OIII]5007/[OII]3727 (O_32),
([OIII]4959,5007+[OII]3727)/Hb (R_23), and [NeIII]3869/[OII]3727. Given the
typical flux levels of [NII]6583 and [NeIII]3869, which are undetected in the
majority of individual CEERS galaxies at 2.7<=z<6.5, we construct composite
spectra in bins of M_* and redshift. Using these composite spectra, we compare
the relationships between emission-line ratios and M_* at 2.7<=z<6.5 with those
observed at lower redshift. While there is significant evolution towards higher
excitation (e.g., higher [OIII]5007/Hb, O_32, O3N2), and weaker nitrogen
emission (e.g., lower [NII]6583/Ha and [NII]6583/[OII]3727) between z~0 and
z~3, we find in most cases that there is no significant evolution in the
relationship between line ratio and M_* beyond z~3. The [NeIII]3869/[OII]3727
ratio is anomalous in showing evidence for significant elevation at 4.0<=z<6.5
at fixed mass, relative to z~3.3. Collectively, however, our empirical results
suggest that there is no significant evolution in the mass-metallicity
relationship at 2.7<=z<6.5. Representative galaxy samples and metallicity
calibrations based on existing and upcoming JWST/NIRSpec observations will be
required to translate these empirical scaling relations into ones tracing
chemical enrichment and gas cycling, and distinguish among the descriptions of
star-formation feedback in simulations of galaxy formation at z>3.
