Generally, no. As mentioned in the comments, phrases like "a tallest mountain" or "a biggest dog" do not sound sensible.

However, the use of "most" as an adverb does not necessarily imply the superlative; it can be merely intensive. From Merriam-Webster on most:

1: to the greatest or highest degree ... (the most challenging job he ever had)

 

2: to a very great degree (was most persuasive)

The first definition implies the superlative, but the second definition is merely an intensifier. The phrase "a most wanted man" (by the second definition) is equivalent in meaning to "a very wanted man".

Generally, no. As mentioned in the comments, phrases like "a tallest mountain" or "a biggest dog" do not sound sensible.

However, the use of "most" as an adverb does not necessarily imply the superlative; it can be merely intensive. From Merriam-Webster on most:

1: to the greatest or highest degree ... (the most challenging job he ever had)

2: to a very great degree (was most persuasive)

The first definition implies the superlative, but the second definition is merely an intensifier. The phrase "a most wanted man" (by the second definition) is equivalent in meaning to "a very wanted man".